Thank you for your thoughts and experience. Obviously Russia is out!
I was rather hoping to take in both Panama and Suez canals. Which points to a world cruise and possibly jump ship at Brisbane then catch up with a flight to Singapore, that would give us a fortnight with family. I know this involves a flight, it's not a problem, apart from the timing. All the world cruises I can find arrive in Oz at the hot time of year. I think, in the end we might have to compromise on timings, but haven't given up yet.