Wow, Jim, I'm glad you're not my careiver! OUCH!
Before I broke down and accepted I needed a more reliable means of preventing mouth breathing I would ball up the corner of my covers under my chin. (I know, Jim, I was swimming in DeNile.) I had read on here that the head falling forward could worsen OSA so I hoped the wadded up covers would help with that too, and it would have if I never moved all night.
I personally wouldn't want to add something uncomfortable and cumbersome to my sleep garb. I wear a homemade chin strap and got rid of my pile of pillows in order to lessen the chance of my head falling forward. If I were to use anything, I think I could tolerate one of those squishy bead pillows maybe velcroed to my chin strap so as to not add another strap around my head or neck. May not totally immobilze my head, but my chin certainly couldn't fall onto my chest.
By the way, I have a family member who has no symptoms of OSA, but when he falls asleep on several pillows then slides down with his head tucked to his chest, he wakes up with a bad headache.