I've used one brand of 50% cotton/50% poly batting (I think it was Hobbs but it could have been from the warm company) and it was incredibly thin. There was also next to no shrinkage after washing. I wasn't terribly impressed with it (I like the wrinkled look) but you could quilt it something like 10 inches apart.
I have a bag of 50 cotton/50 poly batting from mountain mist that looks light and fluffy (much fluffier), but I haven't used it yet so can't report. It only has something like 3 inch quilting space recommended, though.