We were there this December, and some days it was chlly enough to wear a light jacket at night. During the days, it was Tshirt weather sometimes and sweatshirt weather other times.
I noticed lots of FL people saying tha it was a very unusual cold spell, though, so I don’t think you can count of the cool. The FL people were actually excited abotut he chilly week, because it made them feel Christmas-y!
As for the pools, they are always open and they are always heated.