I love linen, loose linen trousers are great at keeping you cool and you can dress them up or down. I have a few long linen dresses I get from a local shop, plain ones that you can add accessory's to to change the look
Also linen tops, can use them as beach wear as well, I have many long ones that are buttoned so can also be used as a lightweight long jacket IFKWIM.
Bright colours are another essential thing for me (inc white), cotton kaftan type clothing helps keep you cool but can add a belt and a woven bag to go out in.
I live in a hot tropical country and we have quite a lot of Batik here, good quality items can be expensive but I prefer cotton to silk, which makes me sweat for some reason and hard to keep pristine! I tend to have longer length sleeves to help protect my skin as well.
One thing I never wear other than the pool is shorts and any kind of t/shirt, I really dont have the arms or legs for either! And I dont posses a backpack
Chunky wooden or colourful jewelry is something else I wear a lot. Silver, never gold just my preference
I wear different heights of espadrilles as well as flat gold/silver/bronze flat sandals and my trusty Birkenstocks in every colour, but tans/light brown go with many things.
Enjoy Thailand all the above I would wear there as well (lived there for a while)