I pre-soak mine according to package instructions, with 1 Tbsp of Tide Free. They don't shrink much. If I quilt well under 2" apart, the quilt top will seize up a bit, giving it that crinkly look, but that also softens it quite a bit. When I quilt way far apart -- 6-8" apart in most places, it tends to stay quite flat & smooth.
I wasn't aware of the poly scrim. Seems like they shouldn't be able to advertise it as 100% cotton with something like that in it. I'm looking to see if there are any other options, but I suppose it would either need to have a scrim or glue to get the cotton to lie flat & form a good bat. I don't know. What did they use to do in the "olden days" before all these chemicals & synthetic fibers came into existence?