when i want a lofty quilt i purchase batts that are 'lofty'
for a large quilt if you are going to use 2 batts they need to be ones that will shrink at the same rate- or be pre-washed (which i personally can not imagine doing)
polyester batts come in lofts up to 1"!
cotton batts tend to be fairly flat- but i have seen a couple that were much loftier than 1/8"...i think the loftiest cotton batt i've seen was 3/8"