I may have been the one (or possibly one of the ones) that suggested the idea of cutting the boxer shorts.

The solution to your problem is simple and it is the one I use...most boxer shorts are seamed fore and aft, leaving the legs as one piece of fabric. Cut along the seams and eliminate one leg. Trim the other so that it is just a rectangle of silk attached to the waist band.

Wear the silk in the front...without the rear to scrunch up and ride up when you sit and shift, it will remain neatly in place, providing a comfort zone and a barrier to scratchy wool.

An alternative solution is simply to detach the front from the rear so that they hang separately. But you will still have the problem of bunching in the seat.

The ideal colour, of course, is black but there will always be some who insist on white or cream.