Good for you, Sue.
I backpacked around the world two years ago at the grand old age of 52. I loved Oz and really recommend Mission Beach, near Cairns. Try the Tree House: really relaxing with a great owner, complete with dog, cats and a donkey. If you have time, try Port Douglas (north of Cairns) and the Daintree with Crocodilus as a great place to stay near the Barrier Reef.
My trip was the best thing that I have ever done and I am now a real RTWB... I'll leave you to work it out.
Regards, Richard