I dont think you have to use anything. I saw my derm. right before I went on vacation and he said I really should use something to protect my lips from the sun. I was doing the leave it alone method when I was on vacation (at he beach in South Carolina), so the sun was intense and I was outside ALL DAY. I didnt have any problems using nothing. My lips didnt burn or anything. Although I am pretty dark-skinned to begin with and dont usually burn so I dont know if that makes a difference when it comes to lips. So in my opinion you dont NEED to use anything.
But I actually saw by far the most improvement while on vacation so it will be interesting to hear about you. Let me know how Jamaica is too cuz that where im supposed to go next spring break with my friends. That is, if I can heal this BS.