I've had good luck, in the distant, distant past when I cared about my underwear, also known as the child-free era, with tanga or cheekie styles that had silicone grippers at the edges to keep them in place on your bum. I can't recall the name of the brands, I am so sorry, because they are all long gone and not replaced. Hanes bikinis serve me just fine while chasing the munchkin hither and thither.
Sorry no more help.
And on 09/23/2011, we were three; husband, daughter, and me!