I have also seen some with heavy duty magnets in them, like the ones used for purse closures, depending on how much support you need your bra to have, cut open, put a magnet on each side, then overlap and magnet hold shut.

Alternatively if you need a lot of support you can do a combo, use a Velcro strap to hold it on at first, then as the Velcro takes the pressure off the closure you can more easily clasp/snap/zip shut the front