Great Lakes Sailing Club, on Wallis Lake near Forster, NSW.
Also Marmong Point in Lake Macquarie (just watch out for sharks!) and Sanctuary Point on NSW South Coast.
Kyeemagh at Botany Bay is great as well, but a lot of swimmers and jetskis can make the shallows very busy.
As you have said, key ingredients are warm water, waist deep, constant 5-10 knots wind.