On the plus side at least you could genuinely say no. Because who the heck would have fat surgery? Your supervisor is a twit. You did the right thing laughing it off. People like that just like to see that they have caused discomfort with their comments. You take that away from them they've got nothing. Best of luck with you surgery, good luck avoiding idiots.
I don't know what it was called but a gym I used to go to had this thing that was like bicycle peddles attached to a kind of water wheel for your arms. It was the most brutal seated aerobic exercise I have ever come across maybe there is a home version of this? I'm sorry I don't know the name of it. Best of luck with your exercise, weight loss and recovery.
My son is also 8 and I have said to him that people like to talk about other people and don't always say the nicest things so I would prefer to keep my private life private and I would appreciate it if he would respect my privacy by not discussing my surgery. I told him that if anyone noticed my weight loss and asks him about it ( I have my mother in law in mind here) that he should just tell them to come talk to me.
My Bmi is 48 and I still have almost a year until I can have the surgery. I guess I have plenty of time to do my research and get my ducks in a row as much as possible.