Stepping down 12 V to 9 V with minimal waste of energy?
You say you need for "backup".

In this case you can use a MOSFET to switch the regulator. In this case you need a comparator circuit or microcontroller.

LM7809 has 5mA of quiescent current. A low power MCU like MSP430 and simple MOSFET will not draw more than that 5mA.