I think it takes a lot of self and couple examination to really know what is going to be best for you and to then find a person that meets those needs.
I don't think I'd even heard of doulas when I had my first, we lived in the UK then and I think doulas are a lot more unusual there. It seemed like society was telling us birth was something that should be between husband and wife. When it came to the crunch, I needed to be induced and even though we thought we'd prepared, we didn't really have a clue and I lost the plot, so they turned of the pit and pretty much demanded I had an epidural before they turned it back on. What I really wish is that I'd asked my mum to come with me, there was no way we could plan for her to be present, as they lived too far away and were working full time, but as I was induced before my due date, they were actually staying with us and ended up taking me to the hospital. I'm pretty confident she'd have got me through without the epidural, we'd been planning a homebirth, but when I found I needed to be induced, my midwife suggested getting an epi before they even started, it was only at my mum's encouragement that I even tried without.
As well as being induced, it was fast, so when planning for my 2nd birth, I seriously considered a doula, but decided in the end that I didn't want to take the risk of them not making it. It turned out to be horrific and I think really was a situation where the epidural was a good idea. It was one of those rare births where a c-section would have been a better outcome, I don't know if a doula would have helped or not. The person I would have used was my postpartum doula and she was very supportive as a processed it afterwards and had I had another birth in that area, I would definitely have used her as a doula, but by that time I knew her pretty well and it would have been more like a trained friend.
We'd moved by the time I had my 3rd and I revisited the doula question and had pretty much decided to skip it because we were planning a homebirth with a midwife and though they were a team of two, they arranged it so we got to know both of them. However, it ended up that I needed a c-section and I did ask a friend to be with me, which was fantastic and didn't hinder anything with my husband, it just allowed him to concentrate on the baby when that was needed and for me not to feel completely alone. There is a lot going on in the operating room and I didn't even grasp things like the sex of the baby without my friend right there talking directly to me.