How to Choose Mattress Firmness for Better Sleep

The Quick Version

• Mattress firmness labels aren't standardised across brands, so a "medium" from one company can feel completely different from another's. The 1–10 firmness scale is the most reliable reference point.
  

• Firmness and support are two different things. A mattress can feel soft on the surface and still support the spine well, or feel rock-hard and still create pressure points.
  

• Sleep position is the single biggest factor in determining which level of firmness will be best. Side sleepers do best with medium to medium-soft, back sleepers with medium-firm, and stomach sleepers with firm.

• Body weight changes how a mattress feels underneath you. Lighter sleepers tend to perceive mattresses as firmer; heavier sleepers compress more and usually need a firmer surface for proper alignment.
  

• The old advice that a firm mattress is always better for back pain has been disproved by clinical research. Medium-firm consistently outperforms firm for reducing pain and improving sleep.

Disclaimer: This article provides general information only and is not intended as medical advice. If you are experiencing persistent back pain, joint pain, or sleep difficulties, please consult a qualified healthcare professional. In Australia, you can speak to your GP, contact Beyond Blue on 1300 22 4636, or call Lifeline on 13 11 14.

Walk into any mattress store or scroll through any bedding website and the same problem comes up fast: every brand uses the same words differently. One company's "medium" feels like another's "firm." There's no industry-wide standard, no universal rating that means the same thing across the board. That makes figuring out how to choose mattress firmness more confusing than it needs to be.

Forget the labels. The three things that actually determine the right mattress firmness are simpler than most brands make them sound: how you sleep, how much you weigh, and whether pain is part of the picture.

What Mattress Firmness Actually Means

Firmness is how soft or hard a mattress feels when you lie down on it. Most brands rate it on a scale from 1 to 10, where 1 is extremely soft, and 10 is harder than most people would ever want. The mattress firmness scale is a helpful starting point for choosing the right mattress, and the vast majority of sleepers land somewhere between 5 and 7, which is the medium to medium-firm range. If you're not sure where to begin with the whole process, firmness is usually the first decision worth getting right.

Firmness and Support Are Not the Same Thing

This is a distinction worth getting right early, because it trips a lot of people up. A soft mattress can still support the spine beautifully if the layers underneath are doing their job. And a firm mattress can still create painful pressure points if it won't let the body's natural curves sink in where they need to.

Whatever type of mattress you're considering, think of firmness as the feel and support as the function. You need both to work together, but they're doing different jobs. A mattress that feels comfortable in the first five seconds of lying down isn't necessarily one that will keep your spine happy for eight hours.

How to Choose Mattress Firmness by Sleep Position

Your sleep position changes where your body puts the most pressure on the mattress, and that changes which level of firmness keeps your spine lined up properly. The research backs this up: firmness, comfort, sleep quality, and spinal alignment are all connected, but the right level depends on how your body actually sits on the surface.

Side Sleepers (Firmness 4–6)

The best mattress firmness for side sleepers sits in the medium to medium-soft range. When you sleep on your side, all your weight lands on two narrow spots: the shoulder and the hip. If the mattress is too firm, those areas can't sink in enough, and pressure builds at the joint. That's the numbness, tingling, or dull shoulder ache that drags you out of sleep at 3 am.

A softer mattress lets the shoulder and hip drop in just enough to keep the spine running in a straight horizontal line. Go too soft, though, and the midsection starts to sag. Medium to medium-soft hits the sweet spot for most side sleepers.

Back Sleepers (Firmness 5–7)

The best mattress firmness for back sleepers is medium-firm. Back sleeping spreads your weight more evenly, but the lower back has a natural inward curve that needs support from below. A mattress that's too soft lets the pelvis sink, flattening that curve and pulling on the lumbar muscles all night. One that's too hard leaves a gap under the lower back with nothing supporting it at all.

Medium-firm gives enough resistance to keep the hips level while still cushioning your body's contours. For back sleepers dealing with lower back pain, this range is where the evidence consistently points.

Stomach Sleepers (Firmness 6–8)

Stomach sleeping puts the pelvis as the heaviest point on the mattress, and if it sinks too far, the lower back arches into an uncomfortable hyperextension. A firmer surface keeps the body flatter and the spine closer to neutral.

Worth noting: the clinical evidence for stomach sleeping is thinner than for side and back positions, and most physiotherapists consider it the least spine-friendly option overall. If stomach sleeping is the only way you can drift off, medium-firm to firm is the safest range, but it's worth trying to gradually shift, and a few small changes to your sleep routine can help with that over time.

Combination Sleepers (Firmness 5–6)

There's no single perfect mattress firmness for someone who shifts between positions all night, but a straight medium comes close. Around 5 to 6 on the scale, it gives the best versatility. Soft enough to cushion the shoulder when you roll onto your side, firm enough to support the lower back when you end up flat on your back. Because you're not fighting your mattress through the night, you're also more likely to stay in those deeper stages of sleep that actually leave you rested.

Why Body Weight Changes the Equation

Sleep position is only one part of how to choose mattress firmness. Two people can lie on the exact same mattress and come away with completely different opinions of it, because body weight changes how the surface feels underneath you.

How Weight Affects What You Feel

A lighter person (under roughly 65kg) doesn't compress the foam as much, so the mattress feels harder than its rating suggests. Going a notch softer usually makes a noticeable difference.

Sleepers in the average range (65–100kg) tend to experience firmness roughly as labelled. Medium to medium-firm works for most people here, nudged up or down depending on sleep position.

For heavier sleepers (over roughly 100kg), the same mattress can allow too much sinkage, and the foam wears out faster under sustained load. Recent research confirms what many people in this weight range already know intuitively: firmer surfaces tend to produce better spinal alignment for heavier bodies, while people with a moderate build sleep best on medium firmness. Firmer mattresses with higher-density foams will make a real difference to both comfort and how long the mattress lasts.

Mattress Firmness for Back Pain and Joint Conditions

If you're dealing with ongoing pain, how to choose mattress firmness becomes less about preference and more about what actually helps you wake up feeling better. This is also where one of the biggest mattress myths falls apart.

The "Firmer Is Better" Myth

You've probably heard it before: a firm mattress is better for a bad back. It sounds logical, and for years even doctors repeated it. But when researchers actually tested it, the results told a different story.

In a well-known trial published in The Lancet, 313 people with chronic low back pain were given either firm or medium-firm mattresses and tracked over 90 days. The medium-firm group came out ahead on every measure: less pain in bed, less pain getting up, and less impact on their daily lives. The firm mattress didn't win on a single count.

That puts a medium-firm mattress, around a 6 out of 10, as the starting point for anyone with lower back pain. And the reason a firm mattress and back pain often go hand in hand is fairly simple: a surface that's too rigid pushes back against the hips and shoulders instead of letting them settle in, and it leaves a gap under the lower back where you actually need contact. That creates mattress pressure points rather than relieving them.

Hip, Shoulder, and Joint Pain

For hip and shoulder pain, medium-soft tends to offer enough cushioning to take the load off those sore spots without sacrificing overall spinal support. Arthritis and general joint pain usually respond well to medium or medium-firm, where there's enough contouring to ease joint pressure without letting the body sink out of alignment.

If chronic pain is part of the picture, it's worth having a conversation with your GP or physiotherapist before deciding. The right firmness can reduce discomfort meaningfully, but it works best alongside proper clinical advice.

When You and Your Partner Disagree on Firmness

Different body types, different sleep positions, different preferences. It's one of the most common bedding headaches for couples, and compromise usually means at least one person is uncomfortable. Research on bed-sharing couples in Melbourne found that roughly one in five awakenings was caused by the partner's movement, which only makes things harder when someone is already on the wrong firmness for their body.

The most practical fix is a split configuration that gives each person their own mattress on their own base. If that's not feasible, a medium (around 5 to 6) tends to be the best compromise for couples, since it sits in the range that works reasonably well across most body types and sleep positions.

How Letto Can Help

This is where understanding how to choose mattress firmness pays off in a practical way. The Letto mattress is built at that medium-firm level the research consistently points to, with 25cm of gel memory foam that provides pressure relief without excessive sinkage. The cooling gel technology helps manage heat through the warmer months, and because the mattress is designed to work with an adjustable base, firmness and positioning complement each other.

There's a reason Australian families keep coming back to Letto.

Two Firmness Levels in One Mattress

For anyone who isn't sure medium-firm is right for them, every Letto mattress features a reversible firmness design. Flip the internal foam layer, and it switches from medium-firm to medium-soft, giving two options in one bed. If preferences change after an injury, a shift in weight, or just over time, the mattress adapts rather than becoming a problem. Our package deals include the mattress, adjustable base, and pillow together so firmness works as part of a complete sleep setup, and with a 30 Night Comfort Guarantee, there's proper time to test whether it's right. Not sure what works for your situation? The team is happy to talk it through.

Split Configurations for Couples

For couples with different needs, the Split King, Split Queen, and Split Super King configurations let each person choose their own firmness and adjust their side independently. No compromise, no spare bedroom needed.

Frequently Asked Questions

What is the best mattress firmness for back pain?

Medium-firm, rated around 5–7 on the standard 1–10 scale. Clinical research has consistently found that medium-firm mattresses outperform firm ones for reducing pain and disability in people with chronic low back pain. A firmness of roughly 6 out of 10 is a good starting point. If pain persists, consult a GP or physiotherapist.

Does body weight affect which mattress firmness I need?

Yes. A lighter person (under roughly 65kg) puts less pressure on the surface, so the mattress feels harder than its rating suggests, and going a notch softer usually helps. Heavier sleepers (over roughly 100kg) compress the foam more and typically need a firmer surface to prevent excessive sinkage and maintain proper spinal alignment. People in the average range (65–100kg) tend to experience firmness roughly as labelled.

Is a firm mattress always better for your back?

No. This is one of the most persistent mattress myths. Research has found the opposite: medium-firm mattresses deliver better results for pain in bed, pain on rising, and day-to-day disability than firm ones. A mattress that's too firm can create pressure points at the hips and shoulders while leaving gaps under the lower back, which worsens rather than relieves discomfort.

What firmness should couples choose if they disagree?

If one partner prefers soft and the other firm, a split configuration with separate mattresses on each side is the most effective solution. Failing that, medium firmness (around 5–6) is the best compromise, since it sits in the range that works reasonably well for most body types and sleep positions. Research on bed-sharing couples has found that about one in five awakenings is caused by the partner's movement, which makes individual firmness control a practical upgrade.