any quilting cottons work well for backgrounds- some people have made fabulous-beautiful appliqued quilts with muslin back grounds. cotton sateen is nice-
why the disdane for broadcloth? i've used some very nice cotton broadclothes and do not know any reason to not use it....although it is heavier than some of the other cotton fabrics used for quilting on a regular basis...i know the poly blend broadclothes may not be as nice---but cotton broadcloth is a very nice fabric.
there are beautiful appliqued quilts with backgrounds that are prints, marbles, batiks...you can use anything you want- it's the applique that will make the quilt.