Cairns local and dive pro here. There's a lot of options suitable for all levels of diver. See
here
Most leave daily or have transfer vessels and visit the Outer Reef. Variety of sites, great experiences and suitable all levels. Gear etc all included.
Trips like Mile Ball and Spirit of Frredon have twice a week departures and have a low level flight one way due to the distance the travel. For more experienced divers but no problem if your Open Water but you would need to take your Advanced on board or at the very least Deep Adventure Dive as most sites tend to be deeper than 18m.
Mile Ball and SOF visit the far north and Ribbon Reefs for 4 or 5 night trips. Expensive but fabulous diving. Book out months in advance so don't leave it too late.
Feel free to drop me a DM if you need any local advice. Doesn't have to be dive related