That would be hard. If I were in your shoes, I would pick someone I didn't know previously. Reason being, you are a doula. if they 'disappoint' (as people can be the biggest critics of there own profession, especially if they are exceptionally good at what they do) then it won't hinder a currant relationship you have. And if they are amazing, then you have added a great contact to your network.
I completely agree with this. Also, I'd feel less awkward getting naked around a stranger than someone I'm likely to have over for dinner, at least until after the fact. I definitely think in-person interviews are the best way to assess a personality match, and being very clear (with yourself and the potential doula) about what you are looking for.
This is tough, but ultimately up to you. Maybe you shouldn't have one since you are one, and I think that if you really did want one there with you, it would be a no-brainer for you? Good luck with your decision!