Use SRAM triggers. They use two thumb levers,so you can work them just as easily if wearing bulky gloves or mittens. You can also keep a finger on the brake lever and still shift normally.
__________________
C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Brompton S6L/S2E-X/M6L-X/S12 T Line