This mattress proved to be excellent for my back. I was skeptical for the ultra firmness but it proved that this is what I wanted. I do not use a spring box and I have it on the floor (sleep with my 2yr son). It helped my back pain disappear and it is highly recommended if you are sleeping on your back. Granted, I'm not able to sleep on my stomach any more but I do not care. It is a thick mattress that adds several inches clearance from the ground. Sitting on the edge doesn't create an issue i.e. it doesn't sank in. It may take a couple of days to adjust to it but I will never go back.