I make this type of pillow cover quite often. I've used plain fabric, upholstery fabric, and, yes, even quilted fabric. I don't like to sew on Velcro -- although I do think it is amazing -- so I put a buttonhole in the center of the top flap before I sew the top and bottom seams of the cover. I have lots of mismatched buttons from my costuming days, so it's no trouble to find a button that will close the pillow cover over the insert. My "rule" of measurement was to add one-fourth of the insert's size to get a nice overlap when it was finished.