Mattresses made today are complete shit, from the $200 dorm-room models up to the $10,000 Ultraname Black Special Editions. We bought a Stearns & Foster ca. 2000, from the middle of their line, and got eight or nine good years from it - in part because it was a genuine two-sided mattress and we could flip and spin it as needed. When it came time to replace it, an equivalent absolutely could not be bought at any reasonable price. Such mattresses had ceased being made except by custom-builders.
Nearly all mattresses today are sold with “no-flip” as a Feature!!! but what that means is the cheap bastards are only selling you half a mattress, one side instead of two.
Inferior cores and springing are being covered with ever-deeper layers of inferior polyurethane foam. Poly foam is, at the structural level, brittle. The bubbles break down over time, and every broken bubble is gone forever, leaving saggy plastic.
Unless you can afford to have a custom mattress constructed the way they were built until the 1990s or so - and you can, at around $12-15,000 for a king size - there is one and only one mattress technology that will give comfort and last more than a few years.
Get a good-quality, three or four layer pure latex mattress and put it on a euro slat foundation. With the mattress seller helping, you can choose layers that are ideal for your body size, sleeping preference, etc. AND you can restack them to adjust the feel - not just initially, but ten years down the road. Latex is many, many times more flexible than poly, so the bubbles break down very, very slowly - no sag, no dimpling, even with heavy use and over years. And the euro-slat base allows you to tailor the support to where you need it AND change the support as often as you like.
We have had our 3-layer/euro slat bed for almost three years. We are pretty big people, and we have two Great Danes that frequently share the bed. The uncovered mattress shows no signs of dimpling or sag. We’ve never had to restack the mattress because we got the mix of layers right from the beginning. The ability to move the support points around to accommodate body changes, even temporary ones, has been marvelous.
Unless you’re looking for economy and are prepared to replace your mattress every two or three years, latex is the way to go. Consider that Europeans have been choosing it almost exclusively for decades, and that innerspring mattresses came into being as a cheap alternative to solid mattresses.
I don’t own so much as a rubber plant in the living room; it’s no nevermind to me what choice anyone makes. But if you really do your homework, you’ll find out that modern mattresses have devolved to oversold, underengineered crap across the commercial spectrum - even, and in some cases especially, at the ultra-luxe-premium end.
(Oh, it’s worth adding that most sellers will have a “latex” mattress on the floor… which is almost always a standard mattress design with one or two inches of latex padding. NOT the same thing. You want solid, genuine talalay latex cores.)