I’ve sat in this seat (not willingly) for about eight flights in a row now to Australia due to travelling with kids.
Take a decent neck pillow, ear plugs, socks, eye mask. It’s a bit late but an Airfly Bluetooth adapter makes the IFE nicer to watch.
In HK you can pay for (just) a shower at the lounge (Plaza Premium) & for me this has always been a game changer in helping to make the flight feel a bit less grim.
If you talk to the desk when doing bags & passprt check, they might be able to move your seats.
I’ve found the leg to Brisbane can be either very full or not very full at all so hopefully it’s the latter. It’s not school holidays so it should be okay ish.