@Eileva
Might be worth looking at the Stitchy range from M-Electronics.
They are an Australian firm making a range of Zigbee modules designed to be fitted behind standard light switches. Being Zigbee they should work with Smartthings although you also have another possible approach as they also link to a Philips Hue bridge which in turn can be controlled via Smartthings.
I am based in the UK and from my perspective here I would actually say Australia has more choices than us poor neglected pommies.
Not only do you have the aforementioned Stitchy products but Legrand a French company also make a decent range of smart switches for Australia and America. (They seem to have zero offerings for the UK.)
I believe Fibaro a Z-Wave option is available in Australia and Fibaro micro modules have an excellent reputation. (Fibaro are available also in the UK.) My own aversion to Fibaro is that it is Z-Wave and hence not able to directly link to HomeKit as well as Smarttings. Stitchy via a Philips Hue bridge is currently exposed to HomeKit as well according to their website.