I found mine on https://doula.org.uk/ The trainees are around £200 which usually includes two antenatal visits, the birth (on call two weeks before and after EDD) and two post natal visits for BF support and general crying on shoulder stuff.
Theres also a thread on here called Home Births and Hopefuls, lots of lovely ppl in there - worth joining just so you can learn from ppl going through it now. I had problems finding a doula but managed to get a local contact through advice from that thread.
Why would you need an Inde MW because of the Twin birth? Bit ignorant here about that sort of thing. Id imagine if you need two MW because of two babies then the NHS would provide you with that. The PCT have a responsibility to send someone to you for a HB whether they agree with your decision or not. Might have to argue with them a bit but a doula can help you with that. Ill have a Doula and a MW if I have a HB. Not 100% decided and its still early so I might still need a medical birth, I might have high blood pressure or blood sugar or any number of things could change.
I just finished meeting my doula and shes great, I told her how I want my birth to go down and she was totally supportive of my wish to have a non medical procedure. Shes a shiatsu practitioner too and theres things she can do to help the process along after 36w, pressure points etc, also during the birth theres points to make contractions stronger and all that. Loving it. Am well up for a yoga/shiatsu/water birth. All being well that is!
It does sound like a nice job to do but I cant see how they make any money. I mean shes on call for an entire month for £350. Im sure she can do other things in that time but she cant be on call for more than one birth. I suppose its more of a calling than a money making exercise tho.