Thank you both for further advice. I'm not getting notified of new posts for some reason and just checked back in to see.
I''m getting the driver board delivered today, and will see how the digital output looks.
If it's not great, the next step would be the proto-shield with mosfets and PWM, but size-wise this will be similar to the uno+driver board so I might have to start looking at the fully custom version...
Many thanks,
Barry.