I can mirror Rottys recommendation of Eva Air (Tawanese based airline) for quality especially in the premium economy for direct flights to BKK.
When I travel back and forth between Singapore and the U.K. I only really book with Singapore Airlines now. I did book with BA once and had a terrible experience so when stuck for 12 hours in a plane I will not travel with them again.
Jetstar are another new(ish) Asian airline and use the main airports (SIN/BKK) rather than the budget terminals that a lot of the other budget Asian airlines do.
You can go direct to the airlines websites or try
Zuji (Singapore) for local connecting flights.
Whilst the following is for Singapore, it is fairly accurate for countries close as a large amount of Singaporeans will be holidaying around national holidays to local destinations and so affect prices and availability.
From Frommers
here.
A steady supply of business travelers keep occupancy rates high year-round in Singapore. However, some hotels report that business travel gets sluggish during the months of July and August, when they target the leisure market more aggressively. This is probably your best time to negotiate a favorable rate. Peak season for travel falls between December and June, with "super-peak" beginning in mid-December and lasting through the Chinese Lunar New Year, which falls in January or February, depending on the moon's cycle. During this season, Asian travel routes are booked solid and hotels are maxed out. Favorable deals are rare because much of Asia takes annual leave at this time.
BA and Quantas code share to Singapore. If people want to go via Singapore then the main airport is
Changi whilst the main airport in Bangkok is
Suvarnabhumi. You should be able to check out airlines flying direct and flight times via the arrival / departure schedules if you so wish.
Remember to take your wellies and a few sandbags though as Bangkok is having quite a few issues, as is a lot of Thailand, with
severe flooding (Bangkok Post).
Oh and I can also reiterate what someone else has said about not flying any route that has a stopover (before or after you board) in India. I did a flight which started in India, stopped in London and when on to New York (I did the London to New York leg) and by the time we were coming up to the US coast the toilets were overflowing and totally unusable.
RB