Update: After discussing with hubby, we have booked his Y flights from LHR to SYD with red roo. We did look at the other OW airlines before deciding this. He was on CX in January and the densified Y seating on their B777 were brutally uncomfortable. CX still has the cheapest fares in March - £670 Y return. BA fares were higher than QF fares (£750). QR fares were similar to QF but not all the flights were A380 - and there are more lounges in SIN than in DOH. Have read good reviews about JL Y seats, but their Y fares for some reason were sky high (over £1,500
) With QF flights, hubby decided not to take QF1 and QF2 all the way, only from LHR to SIN and back on A380, and change to QF81 and QF82 from SIN to SYD and back - this will give him a little bit of time in the lounge at SIN to freshen up before / after the long flights. The upside of QF81 and QF82 is that in Y it is 2-4-2, and the downside is that the planes A332 are really old and the Y seats have not been refurb'ed like they did for the J seats.
PS - Forgot to say that I was able to use my amex offer £200 credit for £600 plus spend with amex travel
We booked the flights through amex travel and they were the same fares as on QF website, but the amextravel website was very clunky. We could not find the flights we wanted at first, and had to jiggle a few times until they appeared.