I love my Tuft and Needle Mattress. I have fibromyalgia, neck and back pains. The mattress is firm enough to support me but gives enough to give a comfortable pain-free night of sleep. It also gives enough support when sitting on the edge of the bed that you don't sink in and slide off. I wake up refreshed and ready to go!
I wish the mattress was an inch wider and slightly firmer. I can see a bit of the boards on my bed frame, which is also king size, and I can't sit at the corners of the bed without almost sliding off.