Hi,
I went to SE Asia (Singapore) with my DS when he was 4 months old and again when he was 7 months old (went to Phuket on our second trip). The good news is it's a lot easier when he was 4 months old. He just slept a lot.
Feed your DS/DD on takeoff and landing, it helps with the air pressure changes.
Bring a sling. Even when my DS was 7 months old, it helped sometimes to have him in the sling while on the plane as they make you take the baby out of the bassinet during turbulences, which is very annoying. Also, we found a sling a lot easier when sightseeing in hot weather. The pushchair just got too hot for him to sit in a lot of the time.
In Bangkok, I would make sure you only drink bottled water and if feeding formula, make sure you use only bottled water as well.
Child safety in cars - Just to warn you that they have a very relaxed attitude towards safety when babies are in cars, which is practically non-existent. We took DS in the tuk tuks several times while in Phuket and they don't bat at eyelid at you just holding the baby on your lap in a not very safe vehicle. That attitude is very common though!
The Thais love babies and would want to hold your LO! My DS got taken out of my arms several times and they would just walk off with him to show him stuff. I didn't mind this at all so just to warn you as this obviously doesn't happen much around here!
Watch the mozzies! I think Bangkok is fairly safe (in terms of malaria) but I would buy something here that is safe to use on babies as again, you might not find a product made just for babies in Thailand. My DS got bitten quite a bit.
I think you just need to go with the flow and enjoy it. I always tell people that even when you go to less 'developed' countries, you have to bear in mind babies are born there all the time so try not to worry too much. Enjoy! We had a great time with DS in Asia and looking forward to taking him there again very soon!
Ax