Exclusive Pumping Question

My LO was born at 11lbs, so we have been supplementing 1-2oz of formula since day 1, as nurses worried I wouldn't be able to produce enough. On day 4, a midwife told me since my milk has come in, to cut formula out completely. I tried to that day, but he was feeding every half hour at bedtime, obviously not getting enough. Now I'm wondering if I can be an exclusive pumper with the formula supplementing? I love my time with him, but I know our schedule won't always be this flexible.