Organic underwear is probably the most important choice for you. It touches your skin for many hours and with socks or boxers - you actually put the pressure of your body weight driving your body cells into the garment. No wonder that skin problems and sensitivities are getting more and more common with conventional (not organic) textiles - these are often sprayed with chemicals.

So...  be good to yourself as well as to environment. You don't need pesticide or insecticide next to your skin. We don't need it in our soils and waters. You might consider also newer fibers like bamboo - stronger than silk, it wicks moisture better than cotton, and deters bacteria quite well. Worth considering.