If you narrow it down to sleep apnea as the cause – with the excellent extra oxygen strategy above – you might also try Negentropic Maxilla Masterwork. This works to directly reshape your Maxilla bone which is the big bone in your skull under your nose. Doing so will radically improve your breathing. There’s some other mentions of sleep apnea in the thread.
I bought it for exactly that purpose (Suspected Sleep Apnea) and it’s helped a LOT. The results were also very fast (noticeable that night, undeniable within a week). It also cleared up my seasonal allergies!
It might also make you prettier, but I’ve been happy to ‘settle’ for breathing easier and sleeping deeper.