I know the answer that I gave you was not the answer that you were looking for - obviously.
Because it never ceases to amaze me how doctors will tell people like yourself, to go ahead and do something, without the foggiest idea, of what? Even worse, If you ask this doctor … “what would you suggest?” the first thing out of their mouth is … “Well, I’m not trained in that area.” DUHA!
With your son’s history and your wanting to continue his physical training, and no medical guidelines from this doctor, be warned that this venture has your son’s health at risk, unnecessarily. Add to that, a “quick buck” opportunist will be willing to sell you on a training program, unscripted, that any professional knows well enough to walk away.
Again. my suggestion would be to relax, take it easy and let your son recuperate at his own speed. Allow his body to heal itself as nature intended. Those months of recuperation will go by quickly and without incident if allowed to.