This is a bit of a strange one. Sydney pretty much insisted that we try it, and I have to say I'm a convert.
We have a couple of tatami mats[1] and a fairly thin cotton shikifuton. The whole thing is pretty firm, but that's kind of the idea. I feel like I definitely sleep better.
Last updated Sun May 22 2022 in Berkeley, CA
1: https://en.wikipedia.org/wiki/Tatami