Yes, mainly go by comfort level.
I'm a birth doula, and one thing I've learned is that certification doesn't mean very much. I think it's important initially, but experience and whether you two connect is the most important thing. For instance, some people think that DONA training is the best, but it really comes down to philosophy. I didn't choose to go the DONA route because I disagree with many of their policies, but I went through a training program that was just as rigorous but with philosophies with which are more important to me.
In choosing my doula for my current pregnancy (and planned home birth), I just met her, we hung out, and I asked her a few questions that were important to me. We connected, so I hired her!
You could also ask about services she provides. Some doulas also do placenta encapsulation, some are skilled in massage, and others will have a birth pool for you to use. My doula is lending me a birth pool, but I hired a placenta encapsulation separately. Good luck!