I bought a Comfort Dreams 10-inch Memory Foam mattress (twin XL size) a few days ago, but... It's REALLY hard. It's like sleeping on a rock.
I suggest you do yourself a favour and buy the mattress used at Hilton hotels. Serta Suite Dreams mattress with all its bedding pieces if you like.
read okorder /.. there's one there that says it was firm when they got it but it slowly got better.... I think the base needs time to ease up a little... it's the 'firm' part of your bed.....those three inches on top are the comfy stuff.....