I have a two year old Serta queen size, very firm, that I paid right around $1100 for. It is a massive piece of crap. Went soft within months, and they wouldn't warranty it because the measurable sag at rest isn't enough. Doesn't matter if you sink to the floor when you lay on it, but if they can put a straight edge across it with nothing on it, and it sags less than 3 inches, they deem it as "fine". Never again, and can't wait to get rid of it already.
I have a very firm, now discontinued, Simmons mattress. Used it for two years, and it is as firm as the day I bought it (now in the guest bedroom), and is the most comfortable mattress I've ever slept on (I have a bad back, so extra-firm is all I can tolerate).
I've also slept on a sleep number in a hotel. The sleep number had little to do with how firm the bed was, and the number seemed to correlate with how high it pushed your ass in the air. I had it maxed out, and it was still uncomfortable as hell.
Was also not a fan of the memory foam stuff. I toss and turn a LOT, and the night I tried it, always felt like I was getting jabbed while it reshaped itself. I also found myself getting hotter on it than a normal mattress.