Hi there!
and Sawasdee kha/ Krup
If you are not into shopping.. but would love to learn culture and lay back on the beach try this option:
Try Koh Chang : (Koh = Island) : :-: :-: :-:
Ramayana Koh Chang Resort
Stay at a Cosy Resort where you also have private beach.
The resort can arrange you a Limo as well upon the request
Phuket or Krabi. :-: :-: :-: Why stay in Bangkok when you have more desire for the beach then. But you should visit the Royal Grand Palace in Bangkok if you have time. It is a must (or at least almost) place to see in Thailand.
I do agree with other member here.. saying that you should visit Ayuthaya. Take a cruise if you want.
Enjoy your staying ! and have a lovely time here.