It is all terribly informative. Here in Britain, we are currently researching the phenomenon of chafing. I have found that there is no quick cure to the problem, other than total removal of underwear. A bold step, yes, but necessary. Contact between buns and fabric only tends to become troublesome when layering is involved, i.e. when more than one garment is involved around the butt area.
Natural fats are a good bet.
Avoid underwear with an inbuilt tendency to ride up the butt cleft. These are essential if emergency scratching is to be avoided in public places.