Just to give another perspective... it can be done without a doula, but you'll benefit from preparing yourself in other ways. We don't all have the same resources or options: no finances for a doula, no birthing centers in your area, and there are some not-so-good midwives out there too, and there are some excellent OBs who will be supportive of a med-free birth. I managed to have a great pain-med free, vaginal birth in a hospital with an OB. But I went into it thinking: Knowledge is power, and I need to think of this like training for a marathon. Yes, it's only one day, but who would just go run a 25k without preparing mind and body!?! And we started talking to the OB early, and kept talking throughout my pregnancy as we learned more good questions to ask.
Start your research, talk to your OB or midwife about their philosophy on interventions and if you're not comfortable with the answer, look for someone who matches your goals. Also ask about how things are handled by the staff where you will deliver: you'll spend a LOT more time with your L&D nurse than your OB! If your healthcare provider is on board, but most of your care will be handled by residents (who are young, nervous and inexperienced, and might be more likely to make reactionary decisions), then build an exclusion into your birth plan that residents/students are not allowed to be involved in decision making in your care, and make sure your provider agrees.
And don't forget that your partner/coach needs to be educated, too! Lamaze classes, Bradley Method... whatever works with your personalities. Some insurance companies even cover Lamaze classes (mine didn't cover Bradley, but either might be covered under "flex spending" if you have it!). Anyone who is going to be in the room needs to be knowledgable and actively supporting you, advocating for you, anticipating your needs, and coaching you through your marathon.