I think the right doula can be helpful if (and only if) you want an unmedicated birth. I did not have a doula, wanted an epidural, and had a great experience with the WHC midwives.
The best thing you can do to prepare for birth is to go in with zero expectations. It’s okay to have preferences, but in my opinion, women who have dead set plans and ideas in their head about what the whole experience is going to be like end up disappointed or feeling negatively.