Not sure if they are available in OZ, but in the US I use:
Henderson Thermaxx Back Zip suits exclusively.
Surfing New England winters, this is the warmest and easiest suit I have ever found.
These days I only use it occasionally, since I have been going to Florida in winter.... but when I do, it's totally amazing.
I have not noticed any uncomfortable water intrusion from the super easy FULL Back Zip.
The Fire Fleece lining limits water movement inside the suit.
Hard to find actually FULL back zips.
Most Surf "back zips" are 3/4 length zippers so they don't open far enough for me to get into, since my shoulders which will not rotate enough.
Henderson actually make suits big enough for me and are super easy on/off
They are Dive Suits, so they go up as big as 7 XL
The biggest difference from Surf Suits is that a 3mm suit is 3mm everywhere, no 2 mm panels under armpit... but they are so soft and flexible that I do not notice the lack of 2mm panels.
They look and wear exactly like surf suits.... but are warmer and more comfortable IMO
I will never own a suit that is not fully lined again.... TherMaxx is fully Fire fleece lined
The Fire Fleece lining makes it super easy to on...
to take it off, I simply unzip it and shrug my shoulders.... it falls right to my feet.
hendersonusa.com/product/thermaxx-mens-back-zip-jumpsuit/ 
I did use my 5mm for a 9'6 Ghost session before I headed south this month