supplementing formula

My baby is exclusively breast fed but she always seems to be hungry. Doesn't sleep during the day. And is up until at least 10:00 every night before she finally passes out. I'm thinking she isn't getting enough milk and want to start to supplement but I'm not sure how. What's the best way to introduce it and what kind of formula is best? She takes a bottle fine she has been taking one since she was a week old so that isn't an issue. Any advice helps!!