Not OP but we sound very similar. I wear a CPAP as well as a night guard. My dentist ordered me a "Max Occlusal Guard H/S Daytime" - it covers my upper teeth, has a hard outer shell and a softer lining. It's very thin and I can use it during the day (as long as I'm not talking) to prevent bruxism. I've used the cheaper Amazon ones - the ones from your dentist are well worth the cost.

My dentist created mine, in house, using his 3D-printer (after scanning my mouth with a stereoscopic camera). I am not sure which type of plastic is used, but I wasn't satisfied with the purchase until we had tried different [softer] plastics.

I prefer/recommend the flexible plastic type, which doesn't last as long but is so much easier to make a habit of wearing (because it is comfortable, unlike the solid plastic which was difficult to <snap> into place around teeth).

The flexible form-fit is so much better than my previous attempt at an off-the-shelf sport mouthguard (the type that you boil and then bite down on == sucks); it doesn't ever fall off my teeth during the night, and requires me to intentionally remove it before morning coffee.

For $350 I get a few years of quality sleep — worth it! I keep a second mouthguard in my toolbox [blue collar electrician] for when I'm experience stress on jobsites...