I am an artist in Philadelphia.
Answer
I spoke with you this morning about the mosses that you would like to incorporate into your works. Here is the book I told you about, which is available in our McLean Library. It is available to PHS members through our McLean Library, among other sources.
Martin, Annie,1953-author. The magical world of moss gardening
http://pacscl.exlibrisgroup.com:48993/F?func=direct&doc_number=000020663
As to your question about thicknesses of sheet moss, there doesn't seem to me to be much if any. There are various cultivars of sheet moss, but I didn't see anything about different thicknesses of the plants themselves, although different cultivars may grow a bit higher or thicker than others. You would be able to buy sheets of different lengths and widths. Take a look online to see what is available and where to get it.
This sounds like a wonderful project. Good luck with it. I hope we will hear about it so that we can see the results.