I make mostly charity quilts and use fluffy poly batting. I use 3.5" piece of fabric which makes kind of a wide binding. I also sew the charity quilts ones on by machine.
I use a flat two inches for double fold binding. I like a very narrow binding, though. I've tried 1 3/4" but that is just a little too narrow to be workable.
I cut 2 1/2" and fold over to make it double. Machine stitch onto the top side of the quilt with 1/4" seam. Turn under, and slip stitch by hand on the back. I also miter the corners.