There is nothing wrong with using a UTH as long as it is regulated by a thermostat. People get into trouble with them and end up with burned snakes because they get their first snake, a fish tank, a heat pad, and think that's all they need because the minimum wage big box store employee who is scared to hold the ball python didn't know any better. I'm rather surprised that pet stores don't push t-stats every time someone purchases a UTH but that would require employee training.

If your landlord won't let you install a window A/C unit then you can always make "redneck AC" - fill some empty plastic soda bottles 2/3 full with water and lay them on their sides in the freezer. Don't fill them up all the way or they'll burst. Then just put the bottle in front of a fan during the hottest part of the day to create a cool breeze.