I bought a cheap Amazon matress (~200 or so) for a guest-room bed. That bed ended up becoming our primary bed and within a year it developed a noticable softspo

I bought a cheap Amazon matress (~200 or so) for a guest-room bed. That bed ended up becoming our primary bed and within a year it developed a noticable softspot + indentation where I sleep (my wife's side is fine, I'm a side sleeper, she's half my weight and sleeps on her back mostly). We rotated it and it was good for another 6 months before the same thing happened. In contrast, our 4 year old Leesa mattress (which we're back on as a primary bed) is fine. I'm sure that I overpaid with the $900 Leesa, but I don't know how to be sure I'll get a durable mattress if I get a cheap one.