Standard 10 Firm Hybrid Mattress with Cooling Cover

I suggest spending some time on: https://www.reddit.com/r/Mattress/ now that said, I had an extreme budget for a guest room mattress that I've slept on 30+ times (and am also a side sleeper), and have been very happy with a (full size)"Brooklyn Bedding Standard 10" full firm hybrid" which was, and still is, under $200 on a website I am not allowed to link to, but will probably be the first result if you search for exactly what I wrote.

Brooklyn Bedding. I’ve had mine for a year with no regrets. I bought the firm with a cooling top. I was leaning towards the medium but based on other reviews I chose the firm. Fortunately it is not a hard, it does have good support and bounce. I sleep on my side and back and any hip or back pain I had disappeared. Im 5’10, 170. I rotate it every month or two.

Brooklyn Bedding Standard hybrid in Medium Firm from Walmart. Had it since early May and I love it.

Brooklyn bedding hybrid, I'm now a big fan of hybrid foam/spring mattresses for support and longevity (our previous memory foam mattress from Ikea now definitely has a person shaped hollow in it)

I got a twin x-long mattress from Brooklynn Bedding. Then I got a second one and now they equal a king sized. I got a set of 2 wood frames from IKEA. And now I have a great king sized bed. Easy to move too because it’s basically modular.