You may need to experiment a little bit, but I recommend starting with a natural fiber mask that's smooth to the touch, like a cotton gauze. If you can, avoid synthetic materials like surgical masks. Make sure the mask isn't stretched too tightly on your face to minimize rubbing. Finally, wash your masks frequently with a gentle "free and clear" detergent. If possible, buy a week or more worth of masks, so you can wear a clean mask every day.