I think it is Mike Ball that does the Cod Hole, arguably Australia's premier dive location - might be others like Pro Dive who do it too, but it's a three-four day liveaboard and pricey too.
The Yongala is reputed to be in the worlds ten best wreck dives, and that's further south, near Townsville.
I reckon you need to have a weather eye as much as anything WW for we are getting into tropical storms season, so do some checking on arrival in Brisbane,
www.bom.gov.au to give you that.
Ironically, I did my PADI in Thailand and have never used a dive company in Oz but the likes of Mike Ball and Pro Dive do have good names.
There's liveaboards which are PADI conveyor lines to some extent and bottom level prices of $300+ with add ons will be indicative of that.
If it's looking a little unsettled weatherwise up about Cairns, it is often quite different in Whitsundays and
www.prodive.com.au have two dive vessels operating from there to do reef and Yongala.
There's also a number of sailing vessels that do two-three day sailing trips about the Whitsundays and you can do diving as an add on with some of them,
www.ozsail.com.au being indicative of them.
It might be worthwhile to get up to Airlie Beach (Prosperpine) and see what the weather looks like being and what is on offer as often great last minute deals to be had.
Try and decide on your destination and have a look now via
www.webjet.com.au to see what best fly prices are for they will be somewhat higher if you just book a day or two ahead, and once seeing best price, book direct with airline.
If weather is dirty up north, you could also consider further south the likes of McKay, Rockhamptom, 1770, Bundaberg and even Brisbane for Moreton Island wrecks artificial reefs as far as locations go.
There's even cold water reefs down NSW and Vic that get dived as well.