My son has problems with this and I have found that he does better with microfiber or modal blends. They are slightly stretchy and don't shift as much. I also size down, which sounds weird but there is less bunching and since they stretch, and they are a boxer-brief style, it doesn't ride up, and they aren't too tight.. I don't know if sizing down would work for women's cut underwear, though, and im not sure what gender you're looking for. For women a seamless boyshort would probably be great, and I have bought them for my non-sensory daughter at inexpensive stores like Target. The easiest way to find underwear with stretch that is also breathable is by focusing on brands and materials intended for athletic activity.