Dans-Ez dance belt; unbranded nylon/lycra jodhpurs; Aigle rubber riding boots. Agree about the stiffness of cotton, I have a pair of Caldene jods that are too restrictive behind the knees. Haven't tried the jeans style breeches you talk about, or Western riding. I would worry a bit about chafing from thick material over the crotch with jeans: I might try American-style riding tights for comparison.
Another thought: equestrian vaulters wear tights and leotards, or unitards, probably with dance belts. For ordinary riding you want more leg protection than dancers' tights provide, but leotards would go well under breeches. Would a thong-back provide enough support to do away with the dance belt? This would remove your problem, balletboy, with the wide waist of the dance belt restricting your middle, and would allow you to feel motion through your crotch and buttocks.[/i]