Houses with out central air and babies

We do not have central air in our house and are trying to figure out the best way to keep babys room cool and keep baby comfortable at night. She is just about 3 months old. We live in an old farm house, and in a state with a lot of heat and humidity. We have a second window a/c unit that we can put in her window, but I'm wondering do I need to get her warmer (fleece?) Pajamas or swaddle for when she is sleeping in her room? What have you done in this situation?