You can use either basic barrier methods such as the condom, or the non hormonal IUD. There is also a newer b.c. pill which is super low in hormones that is supposed to be ok to take while breastfeeding
I used the mini pill. It's only really effective if you take it at the exact same time every day though. So I set my alarm on my phone for 7am. That way it wakes me up, I take my pill ad go back to sleep for half hour til my proper alarm goes off. I never forget to take it, coz it sits right next to my lamp.