Women who haven't had full term pregnancies and nursed infants will usually have nipples which are not very prominent. Injecting hyaluronic acid fillers is a painful proposition, which has a limited longevity and is pricey. I generally recommend my breast cancer patients a visit to a reputable lingerie department, where they sell nipple prostheses, which can you can take on and off, at will.
Some of my patients have told me that their nipple elevation was increased, after nipple piercings, however I can't confirm this. I would consider all your options carefully before proceeding. Good luck.