I use a waist one on DW runs otherwise a leg rope does the trick unless my sup sinks! I have seen the Viakobi ones which look really good and am thinking of getting one myself one day.
just using wetsuit plus legrope plus impact vest for bit of extra float on my sup fishing missions........and a PLB personal locator beacon. But suspect room for improvement
I recon you have it pretty much covered, maybe swap the impact vest for the Viakobi, there are regs here for anything further out than 400m off shore and you have it covered with one small change.
okay will look see at viakobi.......am always slightly terrified when a kay or so offshore. But guess you downwind guys go in little packs......safety in numbers?
I see they selling these ones in NZ for about $175.......don't know how the Aussie specifications relate to NZ pfd regulations......but anything that keeps you alive and breathing is good I suppose
I have a Neil Pryde vest with the underarm zips and a velcro cover. The velcro snags the fabric and stitching under the arms of a wetsuit. So far the damage is cosmetic but it's not a good thing on an expensive wetsuit. Wearing a rash top might help but that's more gear and stuffing around.
Another option with minimum bulk is inflatable. 
