Best mouth mount for you action camera

Easiest you might already have
J-buckle mount

Put some tape on it or put tooth protection on it, see Youtube link further down.

https://www.youtube.com/watch?v=NYUzhjZtUEU

With this one you can still close your mouth, if you are surfing or whatever and dont want water into your mouth when falling etc. It is mor sturdy than the snorkel types.

Screenshot from: https://www.amazon.com/Pro-Standard-Grill-Mount-2-0/dp/B00KCSPDUW

This is the more expensive Pro Standard Grill Mount - The best Mouth Mount according to Kyle Martin.