For pants, I like twill, either brushed or regular. If it has to be stretchy, a knit or interlock will work. My personal preference is always for natural fabrics like cotton, not polyester, but synthetics are cheaper and usually work okay.
Jackets always have a bunch of layers to get the right structure. The outer fashion fabric is backed up with something heavier; you can see that if you check out commercial suit coats. I'm fond of wool and wool blends for jackets. A corduroy might work too, and look a little rustic.
My favorite way to buy fabric is always to go to the store in person and fondle it, and go to stores other than Joann's if it's an option. They've got nice lightweight cottons, as you say, and some good brocades, but for variety and heavier natural fabrics I go elsewhere. (If you happen to be near Denver, Colorado, get ye to Denver Fabrics posthaste. They are my very favorite fabric store.)