I read a book called Breath by James Nestor, it’s all about the benefits of nose breathing. Anecdotally this has completely fixed my sleep apnea/ snoring/ energy levels/ etc. Highly recommended!
I'm not sure if it started this way, but I mostly breathe through my mouth at night due to significant congestion in my nasal passage. If I use a nasal rinse or flonase it helps but if I'm not diligent it regresses immediately.
Give this a shot for a week or two. Just jam these up there. It will be uncomfortable at first but you get used to it. Really opens you up and takes away a ton of resistance in nasal breathing.
I know someone who has to make a "vacuum seal" with their mouth, that is, make some slight suction on the inside so that they won't drool in the night. Is it anything like that?
I had to have my deviated septum surgically corrected back in my late teens before I was capable of breathing consistently through my nose. Even simple things like chewing with my mouth closed were difficult because I couldn't breath well enough with my nose only.
I thought I'd get a freebie there (like when you lose weight just by cutting soda - which I already don't drink. Another freebie lost), but when I paid attention I am breathing exclusively through my nose and to make matters worse my tongue is in the mewing position. So this is already the best case scenario for my weight, sleep and jawline. Bummer.
It helped me. I no longer wake up feeling congested. The impact on sleep was more subtle. I had some prior complications so I wasn’t able to expand as much as the avg patient.
I would also suggest looking into the Oxygen Advantage system. Just finished reading the Breathing Cure by Patrick McKeown, makes some interesting claims but mostly found helpful exercises to retrain nasal breathing
His book "Deep" remains one of my very favorite books of all books, and I've turned a fair stack of pages. It's a different kind of medicine though; for me, it revived my soul, if there is such a thing.