New at snakes, need help with emaciated BP

[Orion8]

Hello all, I have been tasked with caring for my uncle's ball python for the next 3 weeks as he is away on vacation. It is about 18 inches long, and he has had it about 2 months. In that time it has only eaten once, right after he got it. He gave me no instructions to care for it, other than that it doesn't eat. I did about an hour of research about the care of BPs before he brought it over and was absolutely appalled when he dropped the cage off. The cage was about 20 gallons and filled with mulch of some sort which was filthy and stinky, with a terra cotta pot to hide in and a deep glass bowl with about 1/2 inch of scummy water in the bottom. The whole thing was bone dry and there was a heat pad underneath but the mulch was too thick for the heat to reach the snake. I took out the snake, which at first I thought was dead it was so listless. There were pieces of stuck shed all over it's body in patches and it has wrinkles in it's skin all over it's body. I can see and feel it's ribs and spine and the bottom of it is almost concave. I nearly cried when I saw it first. I looked up what to do and gave it a good soak in lukewarm water for the stuck shed, and was able to remove it quite easily with my fingers after a little while. It seemed much more lively afterwards. I also went to the pet store and got another hide and a reptile carpet. I took out all the mulch and the deep glass bowl, scrubbed out the tank with water and a sponge, and put down the carpet. I also used two plastic bowls about an inch deep for water (all I have at the moment, 16 and broke so I prioritized the carpet and another hide). I also put some aluminum foil over the top under the screen to keep in humidity, maybe covering about 3/4 of the top. I also bought 3 small frozen mice, one of which I thawed and dangled in front of it at night, it took it immediately and ate it quickly. The snake arrived on Thursday, fed it that night, and changed the cage today. I plan on feeding it again Sunday night and going to the pet store again Monday as I will have money to get it a heat lamp with infrared bulb and water bowls. I'm trying my best, and I went out and got all of those things because even though it isn't mine I can't stand seeing it in such a nasty environment, hopefully my uncle will take better care of it after I talk to him about it. I'm also going to ask him if I can keep it since I'm afraid it will die if it stays with him ( he had it for 2 month and never looked up how to get it to eat or take proper care of it). Please tell me what else I can do for it in the time being and so sorry for the marathon post, I'm just really worried about the little guy and want to give it the best chance!