My sis used the mini pill, you have to be careful to take it at the same time each day, and use extra protection if you vomit within 12 hrs of taking it, but it is like 99% effective or something if taken properly. Sis ended up pg with #3 while taking it but I think was due to operator error!
Also maybe the Mirena IUD? I don't know if it's ok to use while breastfeeding or not but it's supposed to be good...

Bon