We got a memory foam mattress from amazon for our son and he finds it extremely comfortable. I think it seems to be a little warmer but he does not seem to think so.
The memory foam in a box is very convenient, but the one my son ordered from Amazon had a very strong chemical odor when he first pulled it out. He had to air it out a couple of days before using it.
My husband and I sleep on the purple mattress came in a box - it is wonderful but might be more money than you want to spend