Joan, fabric.com has a nice selection of backing fabrics and broadcloth. I've ordered from the twice, and I really liked the quality of the backing fabrics. I ordered a dark blue and a light blue. Both were very pretty. I've never bought broadcloth or flannel from them.

At my first quilting class,it seams like they told us that if you have to have a seam on the backing it is better to have it in three sections rather than two. I think they said it made it stronger.