Pretty much all the advice here is bullshit, it’s one of the best and safest places in the world to travel, if flying to bangkok, spend
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days there and go explore, it’s an amazing city, then head south, I would recommend headed south east to Koh Tao, Koh phangan and Koh Samui, then you can choose to either fly from Samui to the south west islands or take the boat and bus.
Unfortunately this group is filled with miserable negative people with nothing better to do with their time than moan and crack smart arse jokes.
Pack light, you can buy cheap clothes here as you move, bring a travel card with Thai baht on it to avoid bank charges, and aim for the islands rather than mainland, you will have an amazing time and no doubt start coming back regularly 👍🏼 enjoy.