@turkay1-- My mom has sleep apnea too, I know it's a terrible condition. It prevents sound sleep. A comfortable bed and comfortable bedclothes definitely help. My mom also uses cotton or a cotton mix. I think whatever your husband is most comfortable with, that's the bedclothes you should use. We bought a memory foam bed for my mom and that has helped a lot. Her body sinks into the foam when she sleeps so she is more comfortable. I think you should buy one if you haven't already.
A sleep tip that the doctor told us is to sleep sideways. It prevents snoring and prevents the tongue from getting in the way of your throat so you breathe better. They also have special pillows that make sleeping sideways more comfortable. Try these tips, I hope your husband gets well soon.