I bought a dress, this one: http://www.hottopic.com/hottopic/Clearance/GirlsClearance/Bottoms/Disney+Tangled+Silhouette+Skater+Dress-10213674.jsp
Just in case that link ceases to work though, it's basically a stretchy skater dress with a tank style top. The top portion fits me perfectly, the problem is my big ol' butt takes up too much skirt real estate. I kind of guessed from the picture that I'd need to wear some tights under it, but even with tights you still want your whole butt covered. It's just long enough that when I stand perfectly still and don't move at all, it covers everything. However, if I lean ever so slightly to one side or another or heaven forbid, forward, I'm putting on a free show. So I considered letting out the hem, but there's hardly anything to work with. I also considered adding maybe a wide solid black border around the bottom of the skirt, or even cutting the top from the skirt, inserting a wide black band into the midsection (but that sounded really, really hard.)
P.S. I know nothing about sewing, so the simpler the solution, the better (although I'll probably recruit my mom anyway, who would not consider herself a seamstress but can actually follow easy-moderate patterns successfully.)