I don't have advice on treating existing bedsores, but I know that using an anatomic mattress pad can help or might prevent. A friend was in the hospital and used something called a Conforma Care Pad, which she liked so well she asked and found out that its available to the public. They don't use the medical brand name in the consumer market. You can see them at the link below. I think the green one is the like the hospital version. I own the thinner beige product and love the cushion and support.

Anatomic Mattress Pads