I do mix fabrics as well. Can't always pay the quilt store prices. Could I make a suggestion eweandme? Instead of using yarn to tie your quilt I use embroidery floss. It always looks nicer longer than yarn. Just a suggestion. I use the whole strand. I agree, just feel the fabrics and if they feel stiff and scratchy in anyway I would steer away from them. As you go along you will begin to tell the difference in fabrics. Just go with what you like.
Debbie