pretty much all of my cotton fabrics are the same weight- quilting cottons- the only fabric in my stash that is not the same weight as the rest is some of the muslins- i do buy quality (quilting weight) muslins if using for piecing- but i buy thinner-less expensive muslins to use for foundations.
if i am making a mixed textile quilt the weights may differ- such as using flannels, corduroys, homespuns, denims in a quilt- but normal-cotton quilting my fabrics are all pretty much the same