Does your bike has a front derailleur and do you want to operate both the rear- as the front derailleur with the same hand on a dropbar bike, than you can use a mechanical time trial shifter.
A lot of bikes nowadays come with an electronical groupset. But when you buy / own a bike with a mechanical groupset, than you can use this lightweight and simple solution. Be sure you mount a front- or rear derailleur specific time trial shifter, because of the indexing!
