I’ll add scoring settings for folding: 350/4/1x. Just enough to make folding really accurate and easy.
You can get cover stock (130-150lb weight) cardstock in … well, cover size. 11x17.
I recommend getting the bigger sheets, they’re almost perfect full sheet GF size. Everything I see on amazon is like 80 bucks for a 150 pack… I got mine at a local art store (Sam Flax ATL), you can buy them by the sheet, they come in tons of colors.
My masks were made from this sort of cardstock.