I wear 0.5mm Radiator pants in winter with skins underneath.
You do sweat under them but not too bad with skins on as well.
www.radiator.net/The other thing to look at is product like the sharkskin
http://www.sharkskin.com.au/catalogue/product.php/1/8Fleece lined breathable but warm if you fall in, may be too hot in Qld, I've got a long sleeved top in similar fabric and haven't been able to make a whole run without getting too hot!
Been looking longingly at one of these, Kokotat light weight goretex paddling drysuit, shipped from US works out to be about $700 though! Guess thats not much more than a top of the line wetsuit....but not that much less than a return flight to Maui