I want to improve the way I make contact printed proofs and also potentially do some contact printing of paper negatives.

I am trying to source some frosted anti glare glass, but can only find the gear that the picture framers use (2mm thick). My concern is that this may not be heavy enough to hold everything flat. Would this be OK? Or would I be better off trying to source something that is a bit heaver? OR would it work if I layed two layers of glass on top of each other?