My old man's problem

Hi everyone, some of you maybe know about my father's situation. To remind you, he is nearly 90 years old hemiplegia.

The thing I'm concerned about is bedsores , my father sleeps on matress not a bed.

My old man doesn't feel comfortable at all in the ordinary bed.
Under that I put a large mat. He always move,sometimes we find near the door. We can't communicate with him as he lost everything, sight, hearing, and he isn't aware of anything at all.

While he moves he will be out of the matress and on the mat. Recently he develops some black spots on the shoulder and on his hip, not that big.

I use diapers cream and it's good for redness .
I don't know what to put under him so those black spots would stop.

Thank you guys for your thoughts.