Hi, I would like to join in the topic for breastfeeding!
No need to keep spare formula milk. It's demand and supply. If you have less milk, just latch more often. It is true that breastfeeding is very tiring. Sometimes latch for an hour, you put him down for 1/2 hour, and he's hungry again!
I think the so call low milk supply happens to many people after engorgement. So you wait 2-3 days for the milk to come in, then you suffer from engorgement which is so painful, then your body starts to adjust to the demand which reduces your production. This is the time when many mummies think they do not have enough milk and give up breastfeeding.
Hang in there even if others say that you have no milk. It's the way of mother nature.
I'm still breastfeeding for 18 months and 25 weeks pregnant now, still going strong. [IMG=http://www.singaporemotherhood.com/forumboard/clipart/happy.gif]