I used Burt's Bees Apricot baby oil... I think any kind of oil will do, really. My MIL (who did the cast, and who does body casts of other people as part of her art on a very regular basis, and always uses petroluem jelly) was very impressed.
Since we also did part of my legs (the upper thighs) I put saran wrap over my "girly bits" (I still oiled the hairy parts, but not overly much, just enough to get the saran wrap to stick).
But I didn't bother saran wrapping my armpits, and I do have pretty long (tho sparse) pit hair! I just covered the hair with oil and no hair was torn out!
HTH!
Since we also did part of my legs (the upper thighs) I put saran wrap over my "girly bits" (I still oiled the hairy parts, but not overly much, just enough to get the saran wrap to stick).
But I didn't bother saran wrapping my armpits, and I do have pretty long (tho sparse) pit hair! I just covered the hair with oil and no hair was torn out!
HTH!