Heading to Islands after Bangkok - Which fits me?

Hello im looking for an island or islands that would fit me after my visit to Bangkok.
Im looking forward to swim and relax on beach a lot. Tho from earlier experiences on islands in greek,

I can get bored and need some bar life with markets and other stuff to do. Also I know that some islands can be more expensive the smaller they are.

Phuket,Koh Samui and islands close seem really nice, but that would require me to get an airplane, and that is costly. Are there any islands close to Bangkok that is not completely dead and have a town life on?