I must have been very lucky..all the flannel I have bought from Joannes had minimal shrinkage

Have you tried John Flynn's diagonal pieced backing method? I saw it on another post. I did not look difficult and it might be a good option for you.

Here's the thread:

http://www.quiltingboard.com/main-f1...g-t194847.html

Use John Flynn's diagonal pieced backing. I did that when I had the same problem on a much larger quilt and it worked great.