The most beautiful beach I have ever seen is Eastern Beach on Moreton Island. You'll need a 4WD (or a tour) to get around the island, but it's worth the effort.
When we visited, we were the only ones standing on this expansive sandy beach fringed by crystal-clear water.
Moreton Island is a one-hour ferry trip from Brisbane and is the third-largest sand island in the world. I also suspect it might be paradise.