Stopping pumping will be easier than stopping nursing because you aren't dealing with a baby who doesn't want to quit. You simply drop one session at a time, giving your body about 5-7 days to adjust. I would save the first session of the day, when you are probably the most engorged, for the last one to drop. You probably won't gain weight from this. In fact, I was able to lose the last stubborn pounds after I was done nursing. Just make sure you are no longer consuming those extra calories for making milk. The other issue may be harder, getting your son to take formula. You don't say how old he is. Is he close to a year? When he turns one, he can have regular whole milk. Otherwise, you could have a harder time. Two thoughts. One is that you can add a bit of already mixed formula to the breastmilk and see if he'll take that. If so, you can gradually change the ratio until he is just on formula. Another thing to try is, if you have been giving him the breastmilk through a bottle, you might offer him formula in a sippy cup. They often see it as something different when it comes from a different source. All that being said, I do want to encourage you to try to give him breastmilk for a full year if at all possible. It really is so much better for them. No judgements from me, though. You ultimately need to do what's best for all concerned and what works for you. Good luck!