Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Charlie has developed some concerning habits and I can see that these would be a problem for you, especially when you have knee replacement surgery.
I think it's worth starting with a physical examination and a screening blood panel for Charlie. Changes in behavior and appetite can indicate an underlying illness. Even if he seems otherwise normal early diabetes
may be a problem for him as one example.
Is it possible to put another litter box on the first floor of your home? Perhaps something scared Charlie when he was in the basement and thus his need for you to come with him. By giving him another option at least for a while he may get past this. He is young but if he is overweight perhaps stairs are a problem for him, perhaps he slipped on them and is afraid to go up and down on his own now.
If his blood tests are normal it may help to use a timed feeder so that you don't have to get up and feed him. See this link for an example:
You don't have to feed him much at 4am, just a snack or treat may satisfy him.
Please let me know f you have any further questions.