Going by your picture, you seem very young. (By my old-lady standards! LOL) You've got a lot of life left ahead of you. My advice would be to avoid placing any tattoos in the belly/pelvic region until you're sure you've had all the children God wants you to have. After that, you can reevaluate the area...it may not be suitable for tats at all after pregnancies...or you may be one of the lucky ones that bounces back beautifully and will have a nice canvas for future tats then.

In the meantime...your idea for the lower back sounds really nice!