We got an ikea one, quite comfy

I have a foam box mattress, can’t remember which brand but it’s about 6y old and I find it comfortable. Have previously had sprung mattresses and I find the foam just as comfortable. (Disclaimer- I don’t have back issues so I didn’t have any specific needs). One thing to note, it was a bit smelly initially as the foam degassed, so maybe plan to set it up on a day you can leave the windows open all day so it can air out.

I got a koala then got a topper for it cos my hips still hurt. I should've bought the better mattress with the built in topper. I got the 2nd cheapest of the four koala options. FWIW I am now happy with it. I bought new sheets too, I've got a voucher for $40 off canningvale I'm not planning to use if you want it. I got their sereno linen/cotton blend.

I have an ecosa box mattress and I really like it. You can trial it for a fair while as well.

I don't know if they're still a company or what, but I have a bed frame and mattress (and couch) from Koala. Has lasted a solid 5ish years now.

Bed frame has no bolts or screws, it just pieces together, and the mattress is still lovely to sleep on.

Disclaimer: I did spend a few years before getting the bed frame and mattress on a rotation of airbeds and swags, so take my recc with a grain of salt lol