Just my opinion, I would concentrate on getting the sick one healthy. You would learn about about their health, diet, heat, humidity, dos, don'ts, and other needs before getting a different species. I would spend a lot of time reading about the Sulcata to know all you could know help get this...
To up the humidity mist some water in the enclosure. Can he have a high protein "wet" dog food supplement? My Red-Foot gets a few tablespoons of a high protein "wet" dog food every 2 weeks with her meal. I chose a chunk dog food, (lamb or turkey are the highest protein) I portion it out and...
I would be sure it's a Dude.......if it is a Dudette you should have her checked to make sure she is not egg bound. I am sure Dude is confused as to why he can't come in anymore. I would certainly find out what's wrong. It is his health and he depends on you to take care of his most mal-ordorous...