Arch is the only ballet flat I have ever been able to wear, and I have several styles and colors of them.  Since they are made of only soft leather and rubber soles, with no lining or stiffening, they conform instantly and perfectly to your foot--and that is saying a lot for my sensitive feet!  I have these in beige, and love the perforated airy design so much that I got them in black.  I live in Florida, and these are as cool as wearing sandals.  These do run small; and for some reason, the black ran even smaller than the beige.  This one even ran smaller than some of my other Arche flats, in similar design.  They are pricey; but well worth it.  They are like butter, and last forever--and most styles don't go out of fashion.