Thanks all for your comments so far.
I am travelling with my wife (who has a much smaller BA miles balance) so the WT+ and upgrade option is not really a starter. The plan instead is to bank the miles for both of us and use them for another trip in the future.
BA seems to be the best option - I once went Club JFK-LHR and the flat beds were very comfy.
Any other comments gratefully received but thanks to all so far.
