Quick question - what happens usually if you're not there at sleep time? You might be pleasantly surprised (if you haven't tried this already) to find your absolutely-must-feed-to-sleep baby will go to sleep without the boob if you're not around.

Formula will replace the breastmilk for that particular feed, so to that extent it will affect your supply. But it shouldn't kill it if we're only talking the odd bottle. A bigger risk (if you like) is if your DS decides he prefers the bottles. But again, if it's only the odd bottle it's probably not that likely.

Anyway, don't get me wrong, it's important you get some time out for yourself.