Just use any cotton quilting fabric for the back--something in colors that go with your front. I like to use a backing fabric with some pattern design in it because whatever quilting stitching you do on the front won't match up on the back and something with a pattern helps hide the quilting seams. I also try to pick backing fabric that is the same predominant color of the quilting thread color for the same reason. For example if I plan to quilt with white thread I pick a backing fabric pattern with a white background. Also a printed back will help hide those hard to avoid puckers you get on the back of the quilt. I use warm and natural or warm and white batting. I would avoid a fleece back for your first quilt as it does stretch and may be more difficult to work with. I also usually use the same fabric for the binding as either my backing or outside border as this will help hide any uneven spots and the binding stitching will blend in easier.