Indoor pools in Orlando are few and far between. Heated pools, on the other hand, are very common so you shouldn't have problems swimming unless there is a bad cold snap. In that case you'll be fine until you get out of the water. I would call whatever hotels you plan on staying in and ask if their pools are heated and to what temperature. If you absolutely positively have to have an indoor pool the Marriott Orlando World has a nice one plus beautiful outdoor pools too if the weather cooperates. That's not close to Universal but it's also not a hard drive (about 15 minutes) if you have a car and they have shuttles if you don't.