fleece is much warmer than flannel, so if you want it warmer, I would go with batting and fleece. Take your time quilting and pin the heck out of it before you start sewing the layers together.
The warmest quilts we have are made with white and bright with minkee on the back. All that poly just holds the heat in. They are just the most wonderful quilts for the winter.
I never used to like poly, but I'm so sick of being cold all the time. I'm liking poly more and more.