I suggest you go ahead and split up the stuff into two suitcases. The airport scales might not be the same as yours and if you are even 1 pound over weight they will charge you. Better to be safe than sorry.
Plus, as you mentioned, you won't have any room for souvenirs and I know you will find something that you will want to bring home.
If you are trying to save money by only taking one bag, check with your airline. Most still allow one bag free per customer on international flights. You'll be really happy that you took the extra bag. Plus if there is a cost for the bag, it will be cheaper than the over the limit fee.
Juliann & Jeff
Jamaica Soon Come