As a person who runs cold, and also as a person who prefers to use Warm and Plush over Warm and Natural, I don't think a single layer of Warm and Natural compares to the Warm and Plush. I actually just slept under a quilt with Warm and Natural in it last night, and I was still freezing with the house set to 76. This particular quilt was quilting cotton on top and for backing, W&N for batting. I typically use Warm and Plush, plus a flannel backing on the back now.
Double layer of W&N would probably work for the warmth factor, but as others have pointed out, would be really heavy to wrangle through a DSM, but if you're prepared for it, you can make it work. Earlier this year, I glue basted a layer of Warm and Plush with a layer of Hobbs Polydown and people had recommended using extra glue plus safety pins just to be safe. Possible that was because the poly wouldn't glue baste very well (unsure, because I've never used a poly batt before), but if you were concerned about securing the layers, you could do that. I only pinned every 6in or so? So it wasn't terrible, but if you're going to do that, I highly recommend a Kwik Klip! I didn't have one when I started but you sure bet I went and got one before I finished!
Also, when I glue baste, I do water down the glue a little, but I also use a putty knife (one of those wide scraper tools) to help spread the glue out because it's easy to wash, and less annoying than getting glue all over my finger from spreading it
