A lot of people don't use batting at all with Minkee or Fleece, but I do like a little bit of something even a piece of flannel gives something for the stitches to bite into and can prevent color bleed from the back to top.
Typically I use poly batts anyway with less quilting than is currently popular. Warm and natural is denser and heavier than I prefer for most of my projects (although it is indeed the perfect choice for others), so I just get a really thin batt in a bag instead of my typical fluffy batts.