I recently switched to a full face mask (because of a dental issue) after years of using a nasal mask.
Here is my chin strap of choice: https://www.amazon.com/dp/B08G8Y7PP6?psc=1&ref=ppx_yo2ov_dt_b_product_details
I used it not just as a chin strap but sort of hoisted it up over my mouth to cover it. (also because of my dumb dental issue.) Eventually that didn't work enough and I transitioned to the FFM. But it's a great chin strap and I really like it.
Interesting. I just bought this on Amazon literally yesterday, and wore it for the first time last night. While it helped my mouth breathing I still woke up feeling tired as ever.
Anti Snore Chin Strap | Anti-Dry... https://www.amazon.com/dp/B08G8Y7PP6?ref=ppx_pop_mob_ap_share