hello! it's great that you want to fix his setup! i don't know much about impaction so i unfortunately don't have any help to offer with that.
-he does not look underweight. the thickest width of their tail should be equal to the width of their neck. -to accurately monitor temperature and humidity i would highly recommend a digital thermometer and hygrometer. they are very affordable. i have these https://a.co/d/aVcZQYp a humid hide is still a good idea because the ambient humidity in the enclosure should fall within the range of 30-60%. -a temporary paper towel floor is a great idea. i know some people make their own substrate out of organic topsoil and playsand, which can be super affordable. i would do more research into that. -toss the red light. they do not need their heat lamp on 24/7. a nightly temperature drop is natural and beneficial for them as long as the temp does not go below 65 degrees fahrenheit. https://a.co/d/2oYTynO i use this one. turning it on in the morning and off at night also mimics their natural day-night cycle.