My mom has started developing bedsores. Any ideas?

My mom is almost 92 and in the final stage of Alz. She is completely bed bound, cannot move on her own, incontinent and non-verbal. She has started developing bedsores, the worst is on her butt, but now has one on her hip and starting to get them on her heels. We try to change her position as much as possible but she is in pain on her side and always falls back to lying on her back. We are using patches, med.ointment, position changing and keeping her clean and dry. She also seems to have trouble breathing on her side as she winds up getting face down on the mattress or pillow - we use props to keep her in place but again she still winds up face down. We are using an air pillow to relieve the stress on her butt, but now she is developing sores on her hips (lying on her side) and on her heels. She cannot move her arms or legs so we do that for but her joints are freezing up. Any ideas of what we can do to help her? Her nutrition is poor as she no longer wants to eat, so we keep her hydrated with home-made smoothies (yogurt, fruit, juice and her meds) as this is something she will take. Does anyone have any ideas of what else we can do for her? She is at home under hospice care.