How to choose a mattress
Your weight, your sleeping position, your base and the firmness. Everything else is marketing.
The short answer
Firmness ratings are set for roughly ten to fifteen stone. Under that, a mattress rated 7 feels firmer than 7. Over it, the same mattress feels softer and supports less than the number implies.
Then your sleeping position sets the range: side 4 to 6, back 6 to 8, front 7 to 9.
Start with your weight, because the scale is not absolute
This is the single most useful thing on this page and it is almost never said in a shop.
A firmness rating describes how a mattress responds to a standard load. You are not a standard load. The same mattress is a different bed under nine stone than under eighteen.
| You are | Aim for | Why |
|---|---|---|
| Under 11 stone | One step softer than the position suggests | You compress a mattress less, so it reads firmer |
| 11 to 16 stone | The rating as published | This is who the scale is calibrated for |
| Over 16 stone | One step firmer, and 28cm or deeper | You reach further into the mattress before it supports you |
| Two very different weights | Dual firmness, or zip and link | One surface cannot be right for both |
Then your sleeping position
Side sleepers need the shoulder and hip to sink in so the spine stays straight. Front sleepers need the hips held up, because if they sink the lower back arches all night. Those are opposite requirements from the same mattress.
| Position | Firmness | Pillow height |
|---|---|---|
| Side | 4 to 6 | Highest. The shoulder makes the biggest gap. |
| Back | 6 to 8 | Medium. Fill the hollow at the neck. |
| Front | 7 to 9 | Almost none. |
| Combination | 6 to 7 | Adjustable beats fixed. |
What the constructions actually do
Pocket springs sit in individual fabric pockets and compress independently, so the surface follows your body and one person turning over does not move the other side. Open coil links the springs with wire, so it responds as one surface: a sound, cheap construction for one sleeper and the wrong one for a shared bed.
Foam conforms and isolates movement well, and has almost no air movement, so it holds heat. Its lifespan is governed by density, 48 to 72 kilograms per cubic metre for a decent comfort layer, which almost nobody publishes.
Hybrid means two different things
It covers both a 25mm micro-spring comfort layer over a foam base and a 16cm pocket spring core. In the first, foam supports you. In the second, steel does.
Ask how tall the springs are and what is underneath them.
Spring counts, and where they stop helping
Counts are quoted for a king size, so a double has fewer and a single fewer still.
Above about 2,000 in a king, counts rise by making the springs smaller and the wire thinner. A king is three square metres, so 8,000 springs is one every 1.7 centimetres, and units that small cannot be made from thick wire and still compress usefully.
So a very high count buys fine contouring and excellent motion isolation, at the cost of individual spring strength. A well-built 2,000 spring firm mattress supports a heavier body better than a 6,000 spring plush one.
The words that are not specifications
Orthopaedic is unregulated. No standard, no certifying body, no test. Any manufacturer can print it on anything.
Hypoallergenic is unregulated too, and dust mites live in any bedding.
Natural is unregulated; organic is certifiable, so look for the certificate.
Medium-firm means nothing without a number and your weight beside it.
The base, which voids more guarantees than anything else
Slats more than about 7.5 centimetres apart let a mattress sag into the gaps, and almost every guarantee excludes damage caused by an unsuitable base. The frame creates the fault and then disqualifies the claim.
On a double or larger, a centre rail with a supporting leg. And note that the base changes the feel: a platform top divan firms a mattress and a sprung edge softens it, so the same mattress on two bases is two beds.
Trials, and reading them properly
Firmness is what buyers get wrong most often and cannot be judged in a week. A trial is the only real protection against that, and there are three conditions worth checking.
It usually applies buying direct. Third party listings frequently offer returns on an unused mattress only, which is a different thing entirely.
A stain voids it, and most guarantees with it, so fit a protector from the first night.
An exchange beats a return, because it lets you correct firmness rather than start again.
Free checks before you spend anything
Measure the dip. A straight edge across the mattress: over about 25 millimetres and it is finished, and no topper will fix it.
Measure the slat gaps. Over 7.5 centimetres and the base is the problem.
Check your pillow height. Lie in your sleeping position for ten minutes and have someone look from behind: your neck should be a straight continuation of your spine.
Any of the three can resolve what looks like a mattress problem.
Related reading
Start here
By sleeper
How this site works
Nothing here is paid for by a brand. No manufacturer has copy approval, a preview, or the ability to change a score, and where a link earns a commission that never changes a ranking.
Where a brand does not publish a specification, that is stated rather than estimated, because an absent number is itself information. The corrections log and the products I will not recommend page are both public.
Questions people ask
What firmness mattress should I buy?
Start from your sleeping position: side 4 to 6 out of 10, back 6 to 8, front 7 to 9. Then adjust for weight, because ratings are set for roughly ten to fifteen stone, so under that go a step softer and over sixteen stone a step firmer.
How many springs should a mattress have?
Between 1,000 and 2,500 in a king suits most people. Counts are quoted for a king, so a double has fewer. Above about 2,000 the springs get smaller and the wire thinner, which buys contouring at the cost of strength.
Does orthopaedic mean anything?
No. It is not a regulated term: there is no standard, no certifying body and no test a product must pass, so any manufacturer can use it on anything.
What is the most common mattress buying mistake?
Ignoring your own weight. A firmness rating describes how a mattress responds to a standard load, and the same mattress is a different bed under nine stone than under eighteen.
Does the bed base matter?
A great deal. Slats more than about 7.5 centimetres apart cause sagging and void most guarantees, and a platform top divan firms a mattress where a sprung edge softens it.