You need a chin strap.

I used a nasal mask for years. (now I used a full face mask after a dental issue.) The mouth tape can bother your lips. If you have to cough or sneeze for some reason in the middle of the night? It will be a big problem.

My favorite chin strap was from a company called dwelling with pride. they do not seem to be on amazon anymore. I see similar ones that look like this (that go both over and behind the head.)

https://www.amazon.com/Snoring-Solution-Vosaro-Adjustable-Breathable/dp/B087JL2FGK/ref=sr_1_12_sspa?keywords=anti+snoring+chin+straps&qid=1682001607&sr=8-12-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExUFdVVUo1OFE4RURFJmVuY3J5cHRlZElkPUEwMTIyNTY1MkNRSUg3SlhQTlhTTyZlbmNyeXB0ZWRBZElkPUEwNjc4NzczM0tWTUw4SjBRSjBJTCZ3aWRnZXROYW1lPXNwX210ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

That was key instead of the resmed version which is just the one strap behind the head type.