I would be happy to send you some from my bolt if you like. It's a fleece like material and one side is fusible.
I have used batting or regular fleece in my Bow Tucks and it works out just fine, especially if you're going to do some quilting on the bag. What you use depends to a degree on how stiff or floppy you want the bag. I like a bag with a bit of structure, so if I use batting or fleece I quilt it pretty well with either a medium meander or 1" grip quilting.
Hope this helps!