I totally agree with JCL of Fl. I wouldn't use denim on the back either. I would opt to using a dark cotton, or if you wanted the denim look maybe a chambray.
I just finished a frayed denim and cotton quilt, that could be reversible, with every other square denim for a friend's 80th birthday. It was a real bugger to sew through and to finish. I had made a denim pineapple pattern quilt about six yrs. ago for my son and had really forgotten just how hard it was sewing on the denim, especially the denim that Levis uses. Believe me both quilts are really heavy and difficult to work with. My daughter likes my sons quilt because in the winter she says she stays warm, because she doesn't really move around and get on the cold side of the bed. We have extremely mild winters here in this part of Tx. My son doesn't like it because it is too heavy to sleep under.