Combining milk

Tatyana

I’m wanting to mix breast milk and formula together with my second child who is due next month. With my son I was doing both but then he started throwing up the formula when u would feed him it so we just stuck to breast milk only witch only lasted till he was 6 months old then my body stopped making milk I don’t want the same thing to happen with my second any advice or if u have done this before what was it like for u ?