You gotta join a new tradeskill society at lvl 10 artisan - it is pretty obvious which one it is (the names have hints) - further it's the only one u can join once u hit 10 and have made your choice. Of course u can always go back into your old tier one tradeskill area, too.
If you go the route you are thinking, you can also make leather backpacks and stuff (8 slot).