I think your idea of getting some flannel to play with first is great! Then you will see if you like the way it works. For babies, I have always backed quilts with flannel. So even if you decide to make the quilt from quilting cotton rather than flannel, you can still have a fuzzy side for the baby to feel.
Congratulations on your coming grandchild! and be sure to share pictures when you have decided what to do!