Thanks for the suggestions. Probably September, but still to be confirmed. I think the BKK or SIN routings sound best. Not sure I can be bothered with the AMM or HEL routes. Pricing not too critical as client is paying, and BA J is a known quantity to me.
It's possible I might be needed in SIN as well, if I have enough time, I might try the train. Still trying to engineer the trip to coincide with the Singapore Grand Prix.