They make fairly large kneeling pads that are about an inch thick with hi-density foam inside, covered with sturdy vinyl outside. I think I got mine from Brookstone, it's been a while.
All you'd have to do is put straps on it, so they tied behind your head for the top 2 corners, & at the waist from straps attached at the bottom corners- just wear as a "vest"- it would be too thick for teeth to penetrate, & pretty good airflow, & not heavy. Most PFDs will be awkward, because they're thicker than you need. And leather would be heavy to wear.
I suppose you could just install some pool noodles in a t-shirt?![]()