I live in San Antonio and know exactly what you mean. I struggled for a long time but with the last four batches I found something that works great and is KISS simple. I use a large tub purchased from Wallyworld that is waterproof. I place it in my fermentation chamber/walk-in closet. Put my carboy in there and then put in water about 2/3 of the way up the carboy. I can fit two carboys in mine. This alone only lowers the temp about 2 degrees below ambient so I freeze milk jugs and blue ice packs. I have a pair of each and every twelve hours I'll rotate in freshly frozen ones. I have been able to keep my fermentation down to the low 60's easily when the house was in the low 70's. Gordon Strong says that he uses the same method, in his book Brewing Better Beer.
With my setup I can fit two carboys and float two frozen milk jugs between them. Depending on how much temperature drop I need, I'll use two milk jugs, one milk jug and an ice pack, one milk jug, two ice packs, or a single ice pack--depending upon ambient and upon my target temperature.