My mattress is super firm, and I've never slept better. Others will complain when they borrow it because of how hard it feels, and I understand because it took me some days to get used to, but this is what works for me now. <3
A very old one where I can feel each individual spring, and I have to move around to find a place where they're not stabbing me if I'm sleeping on my stomach. It is very bouncy though, and while it's often just uncomfortable it's strangely fun to sleep on? Probably because I know I'm only sleeping on this until university starts giving lectures on campus again. My mattress over there is a lot more comfortable.