A.Y.
I'm a doula and childbirth educator. I received my training through DONA, which is the most recognized certifying organization. There is also CAPPA, and they have several certifications, birth & postpartum doula, childbirth educator, breastfeeding educator, etc. I don't think you can go wrong with either one. I am only familiar with DONA's requirements.
I would encourage you to become involved with our local doula group, Doulas of Greater Kansas City. That's what I did when I first moved to the area, and they are a wonderful group of women. Our next meeting is Monday the 13th. If you are interested in coming to meet some other doulas and ask whatever questions you have, please PM me and I will give you info on our meeting location. You can also find us on facebook, etc.
Doula-ing is one of the most fulfilling things I do. Let me know if I can answer any questions for you, OK?
Dr. Alyssa