NOT having a doula for my DD's birth is one of my biggest regrets EVER. I could not find one, even though I searched online and so I just settled for reading as much as I could and relying on my husband.
My husband, is yes, great but I had a LOOOOONG labor (28 hours) and he was not taking care of himself because he was *trying* to help me. He barely ate, drank, or even went to the bathroom. I tried telling him to go do these things but he wouldn't go. At my 20 hour mark I was exhausted and he was sleeping and no longer helpful. I was SO MAD. I tapped out and got an epidural, which helped me get the rest I needed to continue dilating and eventually pushing out my girl. He was so fatigued and hungry he almost passed out during my epidural insertion. That bugged me even more. I was blessed with having a great hospital who didn't push ANYTHING on me but they didn't help with pain management by suggesting positions or anything like that.
This time I told him, "we are hiring a doula FOR YOU. So YOU can eat, drink, take a walk, get rest, pee, do whatever and NOT feel guilty." So we are spending $300 on one and I'm looking forward to it. It will be nice to have another knowledgeable woman in the room who can help me, who can help my husband, and make it known that it IS OKAY for HIM to take a break. They can tag team if it's a long labor.
So...having a doula in my opinion is crucial and honestly anyone can be a doula. Your mom, a close friend, a cousin, a sister, etc. just having some OTHER support their so your partner can take a break and not feel guilty because even though they say they are fine...they aren't. I cannot STRESS ENOUGH how important they are because I know how hard it can be without one.
That's my experience. I know some families do just fine with a husband and wife team but in my experience it's a crucial asset to a ~stress~ free, well tended birth.
ETA: I have read stories where women hired a doula and the doula did not participate in the labor. The laboring mother didn't want anyone touching her but every so often she would ask a question and the doula would be there to gently answer and guide her. Hands on support is not the only support. So even if she comes and you don't "need" her but to answer a question here or there, that's still support and that's still beneficial.