Make sure his casque/top of his back is between 80-85* (85*F at the max!), measured with a digital thermometer with a probe, with the probe placed there.
You’ll have to play around with wattages until you get the correct one. Since you‘re in Texas (me too!), Home Depot has plenty of white light regular household incandescent bulbs. These provide a less focused heated area, are cheaper, and last longer than reptile heat bulbs!To what wattage