Warm and Natural is a wonderful product and I have had great success with it. I do pre-wash before using it. It's a nice thickness and weight for most projects.
I would not recommend using such different types of battings in the same quilt (cotton & poly). If you don't pre-wash the W&N beforehand it will shrink some the first time you wash your quilt...the poly will not. Also, the effects created
by the quilting process could produce a very different look/result in each of those battings.