Plexi Art - What Type of Paper?

I've spent a good half hour searching around trying to find a solid answer to this, but anything I find tends to be about lamilabels.

What is the best kind of paper to use for art that goes underneath plexi, spesifically a Razer Atrox?

Where I'm looking to get it done, I can choose from Matte, Silk, and Gloss. Having never done this before, what finish tends to give the best results?
Also, with regards to thickness, are you looking at paper thin, a light card or a heavy card?

Any help would be seriously appreciated, Thanks!