I go to Home Depot or Lowe's and buy plexiglass. (The thin one) It works wonders. It's easy to cut. They have even cut the entire sheet up for me in a couple different common sizes!! I make a sleeve (pillow case) and it slips right inside and looks very finished. You can actually slip the plexiglass out of one cover and in to the next purse you will be using.
It's the best I've found so far!!