A simple, traditional horizontal tricolour of blue, gold and green, with the Southern Cross placed in the canton.
The upper half represents the current flag, with the same shade of blue and the Southern Cross. No need for a separate Commonwealth Star, as four of the stars are already shown in the 7-pointed format to represent the 6 States plus the Territories. The lower half is divided equally in Green and Gold, our national colours.
I have seen similar flag proposals before, but not with these proportions.