Hi There!
I recently booked a RTW F starting in Halifax and stopping in Rome, Singapore and Bangkok plus a 24hr stop in New York City to catch a broadway show.
I would suggest connecting through Montreal and using LH F service from YUL-MUC. then you can connect from MUC-LHR or AMS.
Also Swiss is meant to start flying the new A330 into Montreal sometime in September but nothing has been loaded yet and no offical date has been given.
I would NOT suggest going from LHR-BKK on Thai because they keep switching their 747's from the new seats to the old seats a lot. I read on their board that someone who flew LHR-BKK 5 times had the old 747 swapped out 3 times.
When it's time to go to BKK I would suggest flying to ZRH and then going ZRH-BKK on Thai first class. It's on their newer A340-600.
When I planned my trip I could not get any F on SQ so I doubt that will happen. I did manage to grab a J seat on SQ.
For my route I had no problem finding lots of F available. I'll post my route below incase it helps.
YHZ-YUL AC J
YUL-MUC LH F -> It appears there is ton of F available any day of the week
MUC-FCO LH J -> Stop for almost a week
FCO-FRA LH J
FRA-SIN LH F -> Again, lot's of availability in F. Seems easy to grab. Stop in SIN for about a week
SIN-BKK SQ J -> Getting SQ J was difficult on this route, but lots of TG J available. No F offered on this short flight. Stop in BKK for about 4 days.
BKK-ZRH TG F -> This route seemed pretty easy to get F on.
ZRH-JFK LX F -> This wasn't an easy route to get F. Stop in JFK overnight
LGA-YYZ AC J
YYZ-YHZ AC J
The routes I picked was easy to get F, and as I check now there is lots of availability on these routes in September as well.