Breastfeeding is the best nutrition and food for babies until at least 6 months of age.
However the longer you can breastfeed the better off the babies health will be as well as the better brain development the baby will have.
I've breastfed my babies until age 12 months since I had enough breast milk supply to feed to them and it was a nice bonding experience with my babies as well.
My doctor did say that breastfeeding the babies was best and breastfeeding the baby helps reduce the risk of SIDS by at least 60 percent.
A baby can still die of SIDS even when breastfed but the baby will be less likely to die of SIDS and will be healthier as a result.
But if you don't have enough milk supply for the baby then you can alternate between formula and breast milk when needed.
But allow the baby to breastfeed for as long as possible for the best health.