My advice, and that's all it is, is to keep the cushion/pillow clean, properly fitted (not too tight against the face, and also the 'right' cushion [sometimes you have to try other headgears and masks], and keep the face clean where it rests.

For contact sores, I use Barriere Cream (Wellskin) which is widely available on line and at your drug stores.

Some have found that foam or cloth ridge pads placed around the perimeters of masks really helps. I don't know anything about that, but it might be worth some research and trials. If our hosts won't mind the reference to another forum, try asking at apneaboard.com.