Thanks for all the comments and suggestions!
I thought I had remembered reading that poly batting didn't glue/spray baste very well. Rats. I've also been reading on other threads that a high loft batting also needs some compression while quilting to form stitches well. Going to be an interesting challenge! I pin basted my very first quilt and it was pretty miserable so I never did it again, but per your advice, I'll stick some pins in the stinker when I give it a go.
I've wrangled a few Queen and King quilts through the 6.5in harp so at least I know that I don't lack dedication!
So I had wanted the cloud loft poly for the fluff factor since my 4yo is in love with fluffy right now, but I wanted the cotton so it would shrink and crinkle up better as the poly doesn't shrink. Maybe I'm asking for too much. We can't use wool in the house because Hub is highly allergic and we don't know if the kids have the same allergy - we have no wool around here and don't plan to test this out.
I was going to mark and then FMQ with no rulers. I plan to build another foam insulation topper for the new machine before attempting any of this as soon as I find the time.
Now I'm wondering if it wouldn't just be better to do a layer of Hobbs Polydown instead of the Cloud Loft because it's thinner. I was thinking thicker was better but maybe just not.