Oh, I did not know that piercing the inner surface of the labia would be more painful then piercing the labia all the way through. I thought it was the opposite, LOL! Still I guess the pain would only be short lived. I would not put any weight on it, or tug, just a small ring, or bar.
It's not so much where it is, the pain would be down to the length of flesh the needle has to go through. Like you can get your earlobes pierced in the standard way, or transversely through the whole width.
You could get a surface bar placed there vertically on the inner aspect, they're flat bottomed almost staple shaped bars, so the part inside your skin is flat and less likely to grow out and the ends sit at 90 degrees, so once balls are screwed on each end, that's all you would see.
If you're after an aesthetic only piercing that doesn't affect the way your labia look, I'd think about a Fourchette or a Christina.
You would see the Christina from a distance but they're quite pretty and wouldn't affect your sex life while healing. It's right at the top of your slit and pierced a bit like a belly button. Could get a cute curved bar with a jewel or something.
A Fourchette piercing is through a small piece of skin just below the vagina. The advantage is that no one would see it unless you open your legs and show them. I'm guessing that given where it is, you'd have to be careful during sex for a while but it's one I don't know much about.
I should probably say that I qualified as a piercer a few years ago but only did the course that covered ears, so while I know a bit about other piercings and am happy to advise, you should go have a chat with a professional.