What beds are good to prevent bedsores?

Depends. . There are a wide range of hospital mattresses. The basic ones do little to prevent. Then there are the air mattresses where the pt is sleeping on a cushion of air. This works much better. Really the best help is frequent changing of position to prevent prolonged pressure on one spot for more than 1. - -2 hours .
Mattress Surfaces. It is not the bed but the mattress or surface that is important. There are many choices. Remember that any surface other than a standard mattress will provide improved prevention. Also remember that there are no quality studies showing one surface is any better than any other surface in the prevention of bedsores. Any prolonged body dependency on any mattress can result in pressure injury.
None. Many pressure beds have come & gone.Some are still used for treating pressure sores but as far as prevention a regular 2 hrs turning schedule along with good nutrition, hydration & skin care tops them all.