In my younger days I always wore mens pants for riding in; comfy as the elastic was flatter. Then I got some brilliant "shorts" from M&S but they don't have the same ones any more, they sell the type with looser leg elastic, ok under a skirt but ride up under jodhs. So hopefully I'll never end up in A&E wearing my old ones; they're very sad looking now!
Sloggi do wonderful big pants for riding. The leg holes stay in place rather than creeping inwards so no need for secretive raking to pull them back into place.