Do you wear underwear under spandex?

Well whenever I put on girls regular cotton underwear, and then spandex, i can always see the lines. And I hate that so much. I'm 13, and my mom probably won't let me wear thongs... So how am I supposed to make the ligns go away? Should I even wear underwear under my spandex? Or is that like improper. I know some people who don't wear underwear, but Idk i think its a little gross. Anyways, could you tell me any underwear that you can't see the ligns on your spandex that work for you? Thanks!