Does anyone do formula and breast milk?

Lindsay • Enjoying every second of our beautiful baby girl
My little girl is 5 days old and I had trouble breast feeding while in the hospital so I decided to start formula. My milk came in two nights ago though and the nurse at the hospital had told me to pump until my breasts don't hurt anymore and that I can just feed whatever I pump to her.
Has anyone else does anything like this? Used mainly formula but fed breast milk once a day or so?