I had an all natural birth with neither and it went great as long as you have a good support team. My midwife was amazing at keeping me at ease.
If you don't have good support from your family a doula can be very helpful. However, a supportive mom or sister out bff or even boyfriend/hubby can be almost as good. The difference is that typically doulas have training about childbirth and have worked in the hospital/birth center before and can help you feel more comfortable with policies/staff.
I was just wanting to do classes and I wasn't going to get a doula but not everyone is very supportive about me choosing natural childbirth so I might need one if nobody is going to be willing to talk me through it. I mean girls who even do medicated wanted to give up. I know I can do this but having people support me and be there will make things easier.
You don't need either if you don't want them. I'm justing having my husband and if my family can come then my mom and if my sisters wanna be there they can be. I'm electing to not take any classes, even though my ob keeps telling me to do em. Personal choice, no real reason behind it, just don't wanna. But its not like they'd not let you have the baby if you don't have those things.
You don't have to have a doula ! But I have heard from friends and through research that a doula is extremely helpful during labour and brings a lot of comfort/experience in to the delivery room. It's mostly what you feel most comfortable with, but if you're nervous or your partner is nervous in his role, I have heard a doula can help ease some of that
I've never heard of anyone "having" to have a doula present, but I don't even know what country you're posting from.
Can you call your hospital and find out what they require?