I use this one: https://www.amazon.com/Respironics-Premium-Chin-Strap-P-R/dp/B008MJW18K

10 bucks. Like I said, it aint fantastic but works for me. I don't use very high pressure on my machine and I don't like wearing alot of material on my head ... too hot.

I picked up this one and it's worked well for me. https://www.amazon.com/Respironics-Premium-Chin-Strap-P-R/dp/B008MJW18K