One thought, if you were just short of being able to book business class in points, did you look for availability travelling BA in R class ( World Traveller Plus ) 25% more points than economy but would be a lot more comfortable for the OZ-UK-OZ flights. You would still be in economy on the european sectors.

If you stick with QF9/2 I would recommend 46BC /HJ or 58BC/HJ since these are the exit row seats. As a Platinum member the Premium Desk will contact the seating department and try and obtain these for you. You will be able to get your companion seated next to you too.

Dave