We are in Perth at the moment, come here every year. We took Singapore Airline before, but got disappointed two years ago, so this is the second time we took Emirates Airline. Not too bad, but we just found a better way which we are going to try next time.
AIR NEW ZEALAND is great for space, I am 6ft tall, after sitting down, I still have 3 inches space with front seat, they have the biggest space among all the airlines. But they don't fly to Perth directly, so you can fly from Heathrow to Hong Kong(around £350 return including tax), then take another airline from Hong Kong to Perth, more choices from Hong kong.
Check on internet for the fare.