I have used both felt and fleece as batting. They have both worked for me. I just machine quilted them as I would any quilt. The fleece is very similar to a low loft poly batting and the felt has a little more body than a regular batting but I had no problems with it. I have also used old blankets, too. It really depends on what I am making though. I don't know if I would use it on anything very large.
Try it in a small doll quilt first and see how you like it.