You really need to get a better thermometer. Those strip ones are useless. You need to measure the temp right on the substrate and/or right under the lamp. You need to know what temp the snake is at...not the side of the tank. A simple indoor/outdoor thermometer with a probe (from a hardware store) is an inexpensive and accurate way to go.
You need to heat the hide for your ball. It should not have to choose between being warm and being hidden. This is one reason why UTH are good for these snakes. Also, a UTH will use a fraction of the power that a bulb or ceramic heater will use. If you get the temp set at 85-90 with a UTH, you won't need to worry about day/night.
Any under tank heater from a pet store will work. You want it to be about 1/3 of the area of the tank floor. You can buy a dimmer to control it or you can go with a more expensive (but safer) thermostat. I find that regular lamp dimmers work well.
If & when you do change to a UTH, make sure you control it with something and make sure you give it time to reach max temp and that you measure that temperature right on the floor of the tank.
Good luck with him and welcome to the site.