mixing textures, weights and fibers is PERFECTLY ACCEPTABLE when quilting. if you are concerned about the difference int he weight between one fabric and another you can add a lightweight stablizer to the thinner fabric. i have made quilts with cottons, silks, velvets, wools, canvas, denims, chintz and broadcloth (all in the same quilt) the only thing i worry about when making quilts is how the different textiles will launder together. if it is an item that will be washed i want everything to wash together-if it's a wall hanging i don't worry about that part as much.