mount a direct feed from the battery, actuated by a relay. You will be surprised what output this brings...
measure the voltage that goes into the bulb. I bet it's below 10 Volts, maybe even below 9. If so, you will gain roughly 20 - 30% more light just by adding the relay with direct feed. Put a fuse in between though and take cable that is up for the job (1,5mm? should do it)
Easy to install: dismount the tank cover, dismount the side-panel on the left side, dismount the mudguard (rear) to access to the battery. now connect the new cable to the plus of the battery, strap it to the frame so that it does not hang around and mount it to the front close to the headlight. plug it into the relay's switched port. Now connect the plug from the headlight bulb to the port that switches the relay, make a ground connection and connect the 4th port of the relay to the headlight bulb. If you have done everything right, the headlight switch should still switch the light on, but with way more output.
Same setup for the high beam and you're done. You can use the same power-supply for both relay, as only either low OR high beam are activated, never both together.
HTH