If the driving current is only 12mA and GPIO is 3.3V. Then a 1k resistor with Vsat=0.5V will give: (3.3-0.5V)/1000 will give 2.8mA. With a conservative gain estimation of 10 this should be more than enough current needed.
But would you mind confirming the NPN comment I made above, just wanted to make sure we were on the same page with this?