While I wait to obtain the correct screwdriver/bit to open my CPAP to see if I can fix it (in a prior post), I've been using nose strips and taping my mouth closed. The tape is reaching my skin's comfort limit though, at least using the tape vertically in the center of my mouth (it's the 3M micropore tape in a blue plastic dispenser that I probably got from a doctor visit of some sort, but I also have Nextcare tape).
So far that's been ok, only one time I woke feeling groggy etc. but I might have fallen back asleep after removing the tape.
If I camp or go somewhere for a couple of weeks and don't want to bring the CPAP/don't have room with the other equipment I usually bring, then I do the same.
I was wondering about the soft collars or other 'add-ons' shown elsewhere on this site for "positional" apnea/to try to prevent back-sleeping. I start out sleeping on my side, often in a more-or-less fetal position, but don't know what happens after that besides moving around a lot. I did try the exercise that the wiki talked about and could feel restricted breath.
I can imagine those not being very comfortable, but that's partly the point. I have a wide, firm-foam neck collar from years ago, to rest my neck while upright, but it's larger (my chin rests on it) than the collar shown in the wiki; I was curious how much softer those are.
It would be nice not to have to do anything like that, I checked into an oral device but the test one I was given is very hard to mold because it shrinks after you remove it from your mouth. I even tried putting it over an old dental mold while it cooled, but that didn't help. I decided to wait several more months to see if anything changes with my dental situation. And I don't know how well that surgically-placed device works for most, assuming that would be partly covered by my insurance.