Natural fibers, such as cotton, breathe so I find quilts made with cotton batting to be much more comfortable than poly. As far as your batting, you can pre shrink it, you don't really wash it. You get it wet either in the machine or a laundry or bath tub, then tumble dry. DO NOT AGITATE! Warm and natural has instructions on their website, under wash and care instructions:
http://www.warmcompany.com/wnpage.html