Thanks for all the advice - thought I should give an update. I ended up going with Chawla (responded to email quickly and very professional; FF segment requests entered correctly) like the OP. No dramas with paying by credit card and now have the ticket after Chawla couriered to me.

A very painless procedure for a newbie DONE4 ex BKK purchased from a different country taking about 1-2 weeks from scratch.
The only issue I had was with availability BKK-LHR (on the 4th June QF1 showed D9.. currently D2 in EF; but Chawla could only waitlist me); ended up changing routing via HKG to avoid the waitlist not clearing.