Freestyle actually has uncoated baryta paper that is made for putting your own coating on, so that might be a great choice and something really fun to explore. Thanks for the tip!
i do a lot of coat-my-own, if you want thin ...
if the baryta paper is like some of the stuff i recently bought it is fiber based paper
and double weight, not thin by any stretch of the imagination.
you can get japanese papers, or at your local restaurant supply store some butcher paper
they work great as paper negatives. i also use a pad of "velum" and other glued at one end papers
they are thicker than both butcher and japanese papers, but they also take wax ( paraffin ) well
and can easily be made a little more see-through.
good luck !