A three speed shifter will be fine for a double chainset, just need to set the limit screw on the mech so it doesn’t get the 3rd click. You will need a 9spd shifter for the rear mech though as the pull will be different, compared to a 10spd one.
Ok so the small shifter dropped off my left hand shifter on tue night so im stuck in the big ring, does anyone know if the shifters are the same for double and tripple chainrings and 9 and 10 sp rear mechs? also i cant seem to find a replacement shifter anywhere! ive done loads of work on bikes and never come across the subject? am i stuck in the big ring forever 😯 its a 2×9