Its a long time ago, but when we went we did the over night train to Phuket, it was awesome! Great experience.although far from 5* It depends what you want. Also avoid the time share sellers in Phuket!
I did do the Elephant trecking in Phuket. Im sorry to say it wasnt a very nice experience The elephant was controlled by a 'spear' and had fresh would behind its ear where it had been prodded, uhhh it wasnt nice. Im sure that there are great places to do it, but we got a bad place!
Phuket is amazing, we stayed on Koh Phi Phi for a week too, which was amazing, all this was pre Psunami (sp!) so Im not sure how things have developed, but it is an amazing place. Bankok is brilliant, but after 3 days I was ready for the beach! My advice is to buy a Lonely Planet, well worth it.
If you can manage a trip north, Chiang Mai is great. There's a wonderful place to visit Elephants - its called Elephant Nature Park. You can book to stay there too. There's an amazing market in Chiang Mai too. It's also less crazy than Bangkok. If you can't get there this time, it's a 'must' for next time
I have been to Thailand sep2011. It was amazing I loved it and planning to go again in few yrs. I stayed 2days bangkok then 8 days at Phuket then 2 days at Bangkok from where we have flyed back. I would suggest you extend days at Bangkok as there a lot to do. Best thing for me was shopping for kids.Enjoy; )