Having said all of the above, breast milk is still the best option. Usually, the milk comes in on the 3rd / 4th day. So perhaps, it there is really not enough to satisfy your baby needs, top up with formula. When I said 'top-up', it means to still latch on baby and then continue with formula. This is to ensure that the body is getting the signal to make milk. When there isn't enough, the body will make more. This is the logic behind the demand and supply.
So when your milk comes in on the 3rd day, latch and pump the rest. In order to have constant supply and able to meet his growing needs, especially during his growth spurts, make sure your breasts are emptied 2 hourly. If baby is not hungry or does not wake up to drink, pump it out. Then keep in freezer.
I hope the above helps.