Hi dependent on were in Oz you are going other options for great stop overs are Dubai, Bangkok, KL, Singapore.
I have flown OZ to the uk many times and currently would surgest Emirates or Qatar air ways for value although Cathy, Malaysian, Virgin and Ethad are also good.
Try to get as much of your flight on the new airbus 380 as you maximise you confort the boeing dream liner 777 aree also good, but try to avaiod the older aircraft as the seat layout offer less leg and bum room and on flight legs of around 11 or more every inch counts, if you can afford it bussness is the way to go of priemum economy, some airlines (emirates for example allow you to split you flight classes allowing you to book business on some legs and economy on the rest, also may airline provide cars home to airport if flying BC so factor this in to the cost.
Don't book to early wait for specials, also pre book any internal domestic flight you may need as it cheaper if you do it at the same time as you international flight.
Who ever you decide to book with go to there web site and check your prices compard to any agents it may be cheaper to book your self, also joint their frequent flyer club it will be free and may allow extra luggage ect that can come in handy when you fly back.
Also if you do not whish to wait for your meals, book a special meal, low fat vegeterian, as these meals are served first, that way you finish first and can get to the loo before the after dinner que, lol.
www.seatguru.com
The site address above take you to a site that will allow you to look at all airline seat lay outs for there plans so you can pre book the best seat that suits you.
Hope you go and enjoy yourself, if you have health issue you could also book wheelchair assisted it free.