Arduino: How can one control a 2-wire DC motor with PWM?
A switching buck regulator will just let you provide the correct voltage for the motor (many have a minimum output of 1V3). You should be able to power it off the same supply as the Arduino if enough current is available.

An H-bridge cross-connected to complementary PWM pins will allow you to control the speed and direction of the motor, with 50% duty cycle being no motion. Make sure to use a high enough PWM frequency that the motor doesn't vibrate when at the stop frequency.