Spray some Afrin up your nose before you go to sleep.............
I use Fluticasone (Flonase) whenever my sinuses are clear enough on both sides to snort it. That works well, but I’m clear enough only about 1/4 of the time.
The rest of the time I use phenylephrine pills. That works okay, but not as good.
I only found out about both of these from my sleep doctor after I complained about not being able to breath, in spite of 9 psi from the cpap mask.