3V is the coil voltage. You need to put a resistor in series with a coil to get the "set voltage". Use coil resistance and voltage divider equation to find the resistor value.
Here's a typical circuit for driving a latching relay:
Obviously, ensure that the transistors are only turned on for a short amount of time, as they will sink reasonable current.
- The relay contact is rated for mains voltage, so no problem.