If you are able to keep temperatures proper with just a lamp, that would be fine.
Ambient: 79-81
Cool: 79-81
Hot: 89-91
A under tank heater works well because ball pythons use heat to digest their food. If you use one you must have a THERMOSTAT to regulate the heat it emits. UTH do not change ambient temperatures and is used to create the hot spot.
As for the lamp, buy an infrared one. That way you can leave it on without disrupting your Bp. Heat lamps are rarely used because they destroy humidity which is hard enough to try and maintain using a tank.
Your setup looks good, although of recommend getting another hide. It's a good idea to have matching hides on the cool and hot side so your snake can thermoregulate.