My first piece of advice would be to check out the IBCLC site.
http://www.iblce.org/ You can look at the different pathways, see what classes, how many clinical hours you need, etc... The clinical hours is the part that most people have a difficult time with, it can take several years to get all the hours you need in order to sit for the exam. I encourage people to figure out how you are going to get the hours from the beginning. Otherwise you run the risk of taking all your classes, some have to be taken within 5 years of the exam, and then what happens when it does take years to get the hours.
I am not a IBCLC yet, I have all my classes and hours, the only thing I am missing is actually sitting for the exam. I hope to do that this year depending on how many hours I can get to actually study for the exam. Since it is only offered once a year, it does put a deadline on things. This was not a major career change for me, I am an RN and have been doing breastfeeding support for the last 5 years with a volunteer breastfeeding organization. Exam prep is still labor intensive, and is what I am supposed to be working on right now.
A good stepping stone might to be a CLE or CLC, breastfeeding educator or counselor, there is one program (there may be more but I am only familiar with one) that gives you a CLEC, so the best of both. If I am remembering correctly though, that has to be taken within 5 years of sitting for the exam.