I mostly use the 108" wide backing fabrics, and mostly white or neutral. The back of a quilt just isn't that important to me, especially if it's a wall hanging. I can't bring myself to pay for yardage when $18-$20 will buy enough 108" wide fabric for a backing.
Regarding the extra wide fabric being thin, I have found that in non brand fabric. Robert Kaufman and Moda both have very nice bleached muslin though.