Dearie-
I have given birth to two beautiful, huge babies, the first one with an epidural (he was 10 lb., 2 oz.) and the second one totally natural with zero pain meds (she was 9, 2). I am not a big girl, either- I weigh 140 normally and am 5'10\". It is not a stroll in the park, exactly, but at least for me, it was nowhere close to the -oh-please-stop-the-pain-because-it-feels-like-I'm-going-to-die sort of thing that you see in the movies and hear some people talking about. For the first, the pain was actually worse than for the second, but maybe that was more the emotional circumstances than anything else. With my daughter, I wouldn't even say that it was painful, exactly, just really uncomfortable. It's like your body takes over and it knows what to do to have that child, whether you're along for the ride or not! Now, pregnant with my third child, I'm planning on again going naturally- not that that matters, because the lasting thing is your baby. Birthing: one way or another, you get it over and done with, your body knows what to do, women have been doing this without medical support for hundreds, thousands of years.
One more thing that really gives me solace: millions of women world-over have gone through what you're going to go through... and decide to do it all over again.
Best of luck and best wishes,
Kathryn