Does my pillow or mattress affect my sleep apnea?

To a small degree. Usually what an individual will do is just to find out by trial and error. If their airways closing, their body will assume positions that will keep the throat the most open. You get individuals

who start sleeping on more than one or two pillows. Eventually if it's bad enough they start sleeping almost upright. Usually before it gets that bad somebody is already seeking some sort of medical advice. But once in a while we still find the individual say, "I can't sleep unless I am sitting in the chair." That is bad when you sleep in their Lazy Boy. That's also when they say, every time I lay down, I feel like I am suffocating, and in a sense, they are. It is usual for people to sleep on more than one pillow and then started assuming very bizarre positions. It's called a sniffing position where you pull your chin high up into the air and almost as if you are sniffing something and the reason that works when you pull your jaw up like that it tends to open up the throat just a little bit. Just enough so that a little bit more air can get through and your body will find that position to try and fall asleep. Sometimes you can find people sleeping feet on the floor and head up on the bed. We even find some really strange positions because your body will try to do anything you can to keep the throat open and let you sleep.