I live in South Florida and I run absolutely no heating most of the year. I have a room thermostat set for 84. Central air is set for 89. I provide no belly heat except in my isolation rack which is not in the same room as the rest of my collection. I do not think you will need to do anything special heat wise under your conditions. As long as most of the day is somewhere in the optimal range the animal should have no problem with digestion. Prolonged spikes in either direction are not good. The ones to the higher side are actually more dangerous. It will not hurt for you to provide belly heat but I do not believe it is necessary. I would avoid any kind of heat lamp. More trouble than they are worth. If i were you I would be far more concerned with humidity levels than heat.