My guess would be that the battings would work best if they were at least similar. My experience with wool batting is that it gives more definition to the quilting than cotton or cotton/poly. Plus, it has a higher loft than the others, while being softer. If you were adding blocks all the way around the quilt, even if it looked a little different than the center, it wouldn't look bad, but one or two rows on one side might not being pleasing. I do like to piece together my batting scraps and sometimes I have a little trouble telling one type from another, but I figure if they are that similar, it will work ok. So far so good. But, wool is a different story. I would go for the wool if you feel 90% sure.