As Rat notes in another thread, we here in California don't get the humidity like the rest of the USA. And, after a few too many sun burns, even on hot days, I wear a long sleeve t-shirt and regular levis. Ball caps don't protect my neck well enough, so I always a wear a wide brim hat. That pith helmit you wear would be even better than the cowboy hat I'm wearing in my avitar (signature picture).
After jumping off the tractor onto rocks one-too-many times and twisting my ankles. I now wear work boots of some kind. I just got a pair of tan wellington work boots and like them a lot--quick to put on and take off with out fussing with boot laces and they still seem to protect my ankles just fine. In addition, this area is fairly arid and we get poisonous snakes basking in the heat, so the taller boots makes me feel safer. Don't know if it really is safer, but, I do feel better about it.