Hi there. Great idea to think of a doula. But first may I say that there is nothing at all to be terrified of. Forget all the horror stories that people fill you with. Something to remember is 1. it's called labour because it's hard work, 2. it will hurt and 3. you can do it. Not my advice by the way, but a great book called Birthing from Within - I highly recommend it regardless of how you plan to have your baby. It's not just for "hippy" home births, in fact, far from it!
You must be thinking by now "what a hippy weirdo", but i promise you I'm not. I'm just someone who absolutely refused to believe that it would be as bad as all the mums I knew insisted it would be. And I was lucky enough to have a fantastic, positive experience and the support of a brilliant doula. Sadly she lives in Somerset, so I probably can't recommend her, but I can ask her advice if you like as she teaches doulas in London and may be able to help.
Not sure if you've been on these sites but try
http://www.doula.org.uk/" onclick="window.open(this.href);return false; and
http://www.britishdoulas.co.uk/" onclick="window.open(this.href);return false; All I did was phone a few and on the first site there is a list of questions you can/should ask. I knew straight away that I liked mine and that I wouldn't get on with the others as well.
Having said all that I am now expecting number 2 and am hoping I can recreate the same fantastic experience as last time!!! I am not the only person I know, by the way, who speaks very positively of their birth experience and I think we shouldn't be afraid to share it with people. We quite often get accused of "showing off" as it is more easily accepted that giving birth is a hideous experience.
Please don't think I'm trying to be patronising or blind to the fact that a lot of women do have a difficult time. I am just trying to offer some support and wish you all the very very best. Please feel free to PM me if I can be of any more help!!!
Sorry if I haven't actually answered your question, but I hope it's some help.
Best wishes.