I used the pattern found here. I added two inches to the width and I think three inches to the height (if I remember correctly). I also added a front pocket as requested and side pockets with elastic. And I made the straps a few inches longer and a bit wider. I also made the carrying loop longer.
It is not perfect by any means. I didn't use the piping and that messed up the measurements a little bit I think... I'm not sure. But my daughter loves it, and it works, it's lined, it fits. So it's good.
I can now cross one thing off my to-do list.
In other news, I did finally finish my secret project. It came out nice and I can't wait to show you!