She also said that I might want to consider using
formula for one night feeding, even though otherwise I'll be exclusively
breastfeeding, because PPD is linked to sleep deprivation.

I would seriously consider NOT doing this. Getting a small baby to go back and
forth easily from bottle to breast is not necessarily easy, and adds to the
likelihood of nipple confusion and lower supply, and it seems to me that adding
this needless complication to your life would do away with any of the benefits
that a bit of extra sleep might get you. In my case, skipping a night feeding
would have meant that I'd have just woken up engorged and in pain anyway, so
nothing at all would have been gained. If your baby is one of the ones who
react badly to cow's milk or soy-based formula, matters could be even worse --
while this is a more remote possibility, it's there and should be considered.

Getting extra help so that you can get naps in the early weeks is FAR FAR FAR
more useful. Many babies have day and night mixed up and are up a lot in the
night anyway, regardless of how they're fed at night. There's no way around
peculiar sleep habits in the first weeks or months.

--Helen