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How to choose mattress firmness: a simple guide

How to choose mattress firmness: match it to your sleep position and weight, test it for the length of a trial, and know when to ask a professional.

Camille Laurent4 min read

A mattress in a bright bedroom with a folded blanket on top
Image by HomeoGrapher from Pixabay

Verdict: if you are unsure, choose medium firm. It is the usual middle choice, and it suits many sleepers. The best mattress firmness is the one your body feels supported on after a few weeks.

How to choose mattress firmness depends on your sleep position, your weight and your own comfort. This page gives general guidance. For back pain or a medical condition, ask a doctor or physio.

The decision rule

  1. Find your main sleep position.
  2. Use the table below as a start.
  3. Pick a mattress with a sleep trial of at least 30 nights.
  4. Give it two to four weeks.

Ruling: buy the middle, test it, and move only if it fails.

Firmness by sleep position

PositionOften suits
SideSoft to medium. Lets shoulders and hips sink in
BackMedium to firm. Keeps the spine in line
StomachFirm. Stops the hips sinking
MixedMedium firm

This is a general guide, not a law. Owners often report that comfort is personal.

A person sleeping on their side in a bed with a white sheet
Side sleepers need room for the shoulder and hip to sink inImage by JillWellington from Pixabay

Weight changes the feel

A heavier body sinks deeper into a mattress. That makes a given mattress feel softer. A lighter body sinks less, so the same mattress feels firmer. If you are heavier, a firmer choice is often better. If you are lighter, a softer one may suit.

Couples with different weights face a hard pick. Medium firm is the usual compromise, and some beds offer two firmness sides.

Firmness vs support

These two get mixed up. Firmness is how hard the top feels. Support is how well the whole mattress holds your spine in line. A soft mattress can still support well. A firm one can leave your back unsupported if it sags. A good test: lie on your back, and slide a hand under your lower back. A small gap is normal. A large gap or no gap may mean a poor fit.

Try before you commit

Lying on a mattress for five minutes in a shop tells you little. Sleep on it for several nights. Ask about a trial and about returns, and read the fee terms. A trial is the most useful feature you can buy.

See memory foam vs hybrid mattress for the type decision, and mattress topper or new mattress if your current bed is just a bit too firm.

A medium firm mattress in a simple bedroom
Medium firm is the safe middle choiceImage by congerdesign from Pixabay

Worked example

Say you sleep on your side and weigh below average. A soft to medium mattress will likely feel right. Say your partner sleeps on their back and weighs more. A medium firm to firm mattress likely feels better to them. A medium firm bed is a safe middle for both. A topper on their side is another fix.

A hand resting on the surface of a mattress with a pillow
Lie on it for a few nights before you decideImage by slaapwijsheid from Pixabay

When pain is the reason

If you are shopping because your back hurts, a new mattress may help, but it may not be the cause. Ask a doctor or physio. Do not buy an expensive bed on a promise to cure pain.

Common mistakes

  • Choosing by showroom feel alone.
  • Going very firm because of a belief that firm is healthy.
  • Ignoring the trial and returns terms.
  • Not checking your pillow, which also changes spine position.

Quick questions

What mattress firmness is best for most people?

Medium firm is the common middle choice.

Is a firm mattress better for back pain?

Not necessarily. Comfort and support matter. Ask a doctor or physio for pain.

How long should I test a mattress?

Give it at least two to four weeks.

Does body weight change the best firmness?

Yes. Heavier people sink more, so they often prefer firmer. Lighter people often prefer softer.

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