I nurse my 4 week old son on demand. I want to start pumping to build a stash while continuing breastfeeding but I don’t want to increase my supply too much. How should I start doing this without making too much milk?

I don’t want to have to pump after every feeding either because when I go out I don’t plan on pumping while I’m anywhere but at home. I’m not sure if I’m making sense here.

Also.. how much should I pump from both breasts combined? I usually feed my baby on one side alone and alternate for the next feeding usually every 1.5-3 hours.