Jo and Joy are cute. I have a fondness for Joyce.My favorite NN is Joss, but the nicknames I like usually don't mesh with the favorites on BtN. **Starfish and coffee, maple syrup and jam/Butterscotch clouds, a tangerine, and a side order of ham**
Joss would probably be my pick, too. Though I also like it as a nickname for Joseph. It just has a cooler, slightly edgier feel than the usual nicknames for both.