That's funny you mention that about IKEA because I was about to write something about them. People scoff at them but the most comfortable mattress by FAR I've ever had is from IKEA.
I went to a mattress sales place, I spent £400 on a mattress that in there felt comfortable. What a piece of shiit. I ended up literally giving it away to someone who had a van and who traded me dairy milk buttons for the mattress (it was a large packet).
Anyway I went to IKEA and picked this mattress that was like a burrito. I chose it because I couldn't transport any of the others. I was expecting it to be rubbish. It was £80 I believe. Well, wow. It's the most comfortable thing ever. It suits me perfectly. When they discontinued it, I found out they had simply changed the name and it still existed. So I got it again.
I suppose the biggest decisions are foam versus spring, water air, gel?
So anyway to answer your question. For me, price did not correlate with how happy I was. If you go to IKEA you can sit and lie on them. Not for a few minutes, really sit on it. They have or had a 90 or 100 day return period. So if you hate it just get another.
I have slept on mattresses worth £2000. Slept on ones worth £80. To me, thw £80 was worth £2000. And I mean that.