you can combine anything you want, the only thing you need to keep consistant is laundering requirements...you don't want to mix something you can throw in the washer with something that needs to be drycleaned, or hand washed delicately unless you are going to let who ever know that the quilt needs to be dry cleaned, or 'hand washed'...
i have mixed corduroy's, silks, wools, cottons and fleeces all with great results.