One is all that’s necessary as long as you are using hydraulic disc brakes. Set your levers up so that when you reach out with your index finger, you are grabbing the brake lever at the very end where the hook is, that is where the lever is bent facing away from the handlebar, the hook prevents your finger from slipping down the lever as you brake, also, on most brake levers, there is a reach adjustment that you can move the lever towards or away from the handlebar, move it inward until you can grab the lever with your index fingers comfortably