I have lived here for nearly 2 years and my experience reflects yours. I even had good experiences in Bkk, where a guy just wanted to speak english with me because he had previously lived in England, so he walked around showing me a temple then got me a tuktuk telling me and the driver how much he should charge (something like 40 baht).
Another time I asked an old lady for directions and she physically walked me there (maybe 200 metres) and would not take anything from me to say thanks.
In Ubon a lady at a garage replaced my punctured car tyre and only wanted 100 Baht, she looked astonished when I gave her 200, but it was worth every baht to get mobile so quickly.
I bought the cheapest flight I could to a neighbouring country, which cost about £20. I have read some people say some airlines never check and others scrutinise in great detail, so I would be cautious. The Malaysia flexi plus looks like a great suggestion.
I also read that bus ticket is not acceptable because it is not leaving the kingdom (only to the border).
I was a bit daunted when I arrived in Thailand, but honestly it is not that difficult and like I said if unsure about something the helpful and very knowledgeable people like Brandon will always provide advice, if you decide to do it yourself.
I was quoted 35,000 Baht. This included opening a bank account.
I did it all myself for a fraction of the cost.
Opening the bank account is the tricky part, other than that it is just a case of following a simple process, filling in a few simple forms and providing the evidence immigration require.
It's your choice.
There are lots of helpful people in this group that will help with any questions.
I wouldn't recommend they live on any island as I think it would get boring, but they seem to want to. I think you are correct about Koh Chang being too small.