A respiratory therapist at Kaiser suggested a neck pillow, the kind used on airplane trips, worn backwards, but I cannot tolerate anything pressing on my neck in the front.
So I made a Donut pillow, very lightweight, from a stocking stuffed with spun polyfiber (quilt batting), and covered it with a soft cloth for comfort next to my face. I tied the ends of the fabric so i could try out the pillow.
It is working so well I haven't even bothered to sew it together yet to finalize it. The tubing goes through the middle of the donut, helping it stay in place (and not tug to the side) and the pillow goes in my chest when I'm lying supine, as i do when I'm using the CPAP.
I start the night with my chin on the pillow which keeps my jaw in a closed position, press my tongue to the back of my upper teeth, and seldom have to reposition the pillow. Having adequate air at night has helped decrease my mouth breathing. When i sleep without the CPAP, I'm a mouth breather again.
How to clear the nasal passages due to sinus problems or mild deviated septum problems was a long process, but i ended up having good success with neti pot and therapeutic grade essential oils .