Can I please recommend that you not stay in BA for the holidays? It's horrible here...
Last year I was here for Christmas and New Years and I had to keep all sharp objects out of my reach otherwise I would have slit my wrists. It's not a big celebration down here like it is in the States. You might see a strand of lights every 5 blocks and if you want to find Christmas ornaments and the like, there are a couple stores that sell it, but it's all smaller lights. Oh, and don't forget the fact that if you hear something like bombs going off outside, those are just "fireworks." It's going to sound like a war zone so get prepared. This year, I'm going back to the states, I don't care what the cost of the ticket.
Go to Rio for the New Year, I heard that place gets nuts!! This is just my opinion so take it with a grain of salt...