You could always try Electronize of course.

I would recommend using exactly the same relay, the success of the FR15 series has been due to the selection of the relay plus some other software mods. In fact some users have found the performance of the FR15 better than the FR30, it's not just the current rating but also the voltage rating of the contacts. The FR15 has been better able to cope with the back emf voltage from the motor especially when changing motor direction. Coil voltage does have to be 6V of course.