The maritime jurisdiction maps published by Geoscience Australia may help, Geoff. This is the relevant one (warning: big fat file): https://d28rz98at9flks.cloudfront.ne.../AMJ_69717.pdf
Let me know if you can’t open it.
Key points:
The territorial sea extends 12nm from the territorial sea baseline, which is generally a line along the low water mark at the lowest tide of the year but there are ‘closing lines’ across bays and inlets. The baseline is the black line on the map.
The territorial sea is the greyish fat texta line next to the black line.
But fun key point for Queensland: Queensland includes all islands within 60 miles (I assume nautical but I’ve never tied off that loose end) from the mainland. Each of those islands has its own baseline and ‘generates’ a 12nm territorial sea. You can also see some (most) of those in the map. Note, therefore, that there are gaps between some of the territorial seas generated by those islands and the territorial sea generated by the ‘mainland’, because some of the baselines of those islands are more than 24nms from another baseline.
A common mistake is to assume that Australia’s EEZ is its territory. As you know, it isn’t. Australia has some sovereign rights over the EEZ, but does not have sovereignty.