The standard Uncle Mikes full size grip works great, but not as concealable. My choice for 357s in the 640. For concealability, the 640 wears Altamont boot grips and the 642 keeps the stock boot grips. See a good discussion on Stephen
Camp's Browning site: Getting a Grip
Anthing that covers the backstrap with rubber will make shooting less painful but less concealable. Wear big pockets.