Here is my latest yoga matt bag. I really love this one. It has two straps and a zipper. My last bag was just a bit too small for the thick pilates matt that I have. It was really hard to get my thick matt in and out of the bag; however, I have a thin yoga matt and it is fine in the other bag.
This is the "Purses Bags & Totes" pattern by Cindy Taylor Oates. I made a few changes to the pattern though. I didn't quilt the bag with batting in it. Instead I lined the bag with nylon windbreaker type material and I made cloth straps to go around the bag instead of webbing. You could easily add a pocket to the outside of the bag if you wanted. The ends of the bag also have a sun embroidery on them.
I got the pattern here from SewThankful and I was really pleased with their service.