After reading and re-reading your post, I am wondering if you might consider inserting a flannel wholecloth blanket rather than a batting. It sounds like you are not wanting to actually have your stitches go through all three layers of the quilt sandwich....
" Also, I am intending to space out the quilting as much as possible as I am hand sewing in a hurry. For previous quilts I used wide-spaced pocketing on the back and just a few little hidden pegs of stitches on the front, and I like how it looks; I don't want the front to look quilted and I'd like to do a loosely spaced pattern of hearts on the back that wouldn't work with the squares on the front. So this batting needs to have it's own structural integrity as it won't be seriously sewn down. That seems to work fine for cheap polyester, would it be a problem for cotton? Is it important for the cotton to be sewn into pockets both sides - i.e. for the stitching to go through the front and the back? There seems to be huge variation on the recommended spacing, but at least there are guidelines on the packets! "