Right now LO is on fortified breast milk (so we mix 1 tsp per 4 oz of breast milk to add extra calories since he was a preemie). So I'm not opposed to supplementing with formula... I'm actually strongly considering it for when I go back to work when LO is 3 months old. It takes me 25-30 minutes to pump enough for his next feeding and I think I would need to do 3 pump sessions at work to meet his demand so it's looking like supplementing might be the best route. I still want him to have some breast milk but I don't think I can realistically devote an hour and a half (plus washing pump parts) during the work day to pumping, even if I worked while pumping.

How do you supplement? Is one bottle all formula and another all breast milk? Or do you mix them so that each bottle is half and half?

How quickly do you go through formula?