Echoing the recommendations to go to a reputable piercer who is good at proper piercing placement and jewelry selection. I use titanium for all of my piercings because it is one of the safest least reactive metals. And, aftercare is the most important part of a piercing. Even given the best piercing and aftercare, it is very common for navel piercings to fail to heal. I recently retired mine after trying very hard for 15 months to coax it into healing, but no go.

I don't think a navel piercing is a big deal from a "morality" or "nice girls don't...." point of view. They are totally mainstream with most folks under 40 and with many folks over 40 as well.

Then again, maybe I'm not one to talk. I've got 10 piercings, only 4 of which are above the neck and publicly visible. You do the math.