Fx, have you thought about hiring a doula? I gave birth hoping to have a med-free birth in a hospital last time, with a fairly intervention-happy OB, and my doula made me feel so much more confident. She knew what I wanted and I knew that if I wasn't in a place to speak up for myself, she would do it.
I agree, go in with a birth plan, and try to remember who cares what they think of you. By their next shift they won't even remember, they have so many patients. It's your right to refuse any intervention and you can ask them to not even offer. If it's an emergency, you will know, no one will be asking permission then.
Also, I have a bunch of friends who have given birth med-free in hospitals all over the US, including in ones with very high C section rates, so it is very, very possible.