A mattress is one of the few purchases you can't really evaluate from a spec sheet — lying on it for two minutes in a showroom tells you almost nothing about how it'll feel after eight hours, every night, for years. Here's what actually matters.
What's inside
Nearly every mattress is built the same way underneath the cover: a support core at the bottom (either steel coils or dense foam) that determines the overall feel and how well the mattress holds its shape, and softer comfort layers on top that determine how it feels against your skin in the first moment you lie down. A mattress can have an excellent support core and still feel wrong if the comfort layers on top don't suit you, and vice versa.
The main types
Innerspring — a coil support core with a comfort layer on top. Generally the most breathable (air moves through the coils) and often the most affordable, but can transfer more motion between two people sharing the bed.
Memory foam — foam all the way through, contouring closely to the body. Good motion isolation and pressure relief, but traditionally sleeps warmer than innerspring, though many modern foams are designed to reduce this.
Latex — similar contouring to memory foam but with more bounce and typically better temperature regulation. Usually pricier.
Hybrid — a coil support core with foam or latex comfort layers on top, aiming for a middle ground between support, motion isolation, and breathability. The most common type sold today.
Firmness is not standardized
Firmness is usually described on a 1–10 scale, but there's no industry standard — a "medium" from one brand can feel noticeably different from a "medium" at another. Firmness ratings are only really useful for comparing mattresses within the same brand, not across brands.
As a rough starting point: side sleepers generally want a softer mattress that lets the shoulder and hip sink in enough to keep the spine straight; back and stomach sleepers generally want something firmer for support. Body weight also shifts this — heavier people typically need a firmer mattress than the "recommended" firmness for their sleep position to get the same feel.
The trial period matters more than the showroom
A couple of minutes lying on a mattress in a store, fully dressed, in the middle of the day, tells you very little about how it'll feel after real, tired, unconscious use. Most direct-to-consumer mattress brands now offer trial periods of 90 to 365 nights with free returns — that trial period is doing more real evaluation work than any showroom visit, and it's worth prioritizing over a brand that doesn't offer one.
The one thing people forget
Check the return/exchange policy for firmness, not just for defects. Some brands only accept returns for manufacturing problems, not simply "it's not right for me" — which defeats much of the point of a trial period if you don't actually confirm what it covers before buying.