The only thing that makes your body make more milk is baby nursing, so try offering all the time, like every hour for awhile during the day, and maybe you'll see some improvement in supply after a couple of days. You may lose some of the "sleeping through the night" hours, if baby needs you more for awhile. Let your baby use you as a pacifier instead of a paci, if you have a paci, and skip any supplementation for awhile, so that your lo is hungrier at nursings. Your LO will not starve if you don't supplement- there will be more demand nursings to trigger your body to make more. And whatever you do, don't judge the amount of milk LO is getting from the amount you pump- babies are SO much more efficient. My 11 mo old DS gets plenty to eat, but I'm a horrible pumper- like 1 or 2 oz at a time and I know that he is getting 6-8 easily when he nurses! I think sometimes pumping is incredibly misleading for us. Definitely keep drinking plenty of water.
All that said, if you don't see improvement in a couple of days, follow your instincts! If you are still feeling like your baby is not getting enough milk from you and your lactation consultant and doctor agree, despite any attempts to increase your supply- you're not a horrible mama or a failure for feeding your baby formula, because the alternative (truly starving to death) is far worse than formula could ever be. It was created for a reason.