First of all, it sounds as if it's possibly incandescent, which will fluctuate the water temp drastically enough to cause harm in a betta. Without a thermometer, there is no way to know how much of a fluctuation is happening, or even when. Fingers don't make good thermometers.
It's good that the room temp is warm, but that also will not keep the water stable in temp, so a thermometer is very important, I would strongly suggest you invest in one. The stick on ones go on the outside of the tank/bowl, above the gravel line and below the top water line. They're easy to read, accurate, and inexpensive. Look with one that has a range from 70 - 90 degrees. These are your danger zones... but anytime you see a fluctuation of more than 1 degree, this is reason to be concerned and hard on the fish.
For other foods you can try daphnia, live black worms, frozen blood worms, live or frozen brine shrimp, and small ram's horn snails. Most bettas will eat most of these foods, and if they are alternated (a different food each day) you'll be sure he's getting the best in nutrition.