First thing to decide is when your thinking of going as there are differing weather patterns on the different coast lines of Thailand. Nov-March is the better time to visit the western Andaman coast line, islands such as Phuket, Phi-Phi, Koh Lanta and the mainland areas such as Krabi and Khao Lak. If you're thinking of going in the British summer then you will likely get better weather on Koh Samui, or mainland resorts like Hua Hin or Pattaya. These are not hard and fast rules - I've been to Samui and Hua Hin in Feb and seen good weather. In addition tourists also visit Bangkok and areas of Northern Thailand such as Chaing Mai and the Golden Triangle.
Koh Samui is a large island and as such has a number of resort areas on it from the developed and lively Chaweng and Lamai beaches to quieter resorts such as Maenam and Cheong Mon. The same is true of Phuket, its largest resort Patong is brash and lively, beaches such as Karon and Kata are considered a bit quieter and its possible to find very quiet areas such as Nai Thon and Cape Panwa.
Thailand is well suited to DIY. Low cost flights and carriers serve many airports within the country to reach such places as Samui, Phuket Krabi. Samui is a bit more expensive to get to as the main carrier to the island Bangkok Air also own the airport. Trains serve some areas and long distance buses are available. Most tourists come in via Bangkok, but I've done it via Kuala Lumpur (Malaysia) and Singapore as well which adds options for whoever might be doing good value long haul flights. Air Asia X for example do a low cost service to KL which connects into the extensive Air Asia network of low cost flights. Its also very easy to multi centre your holiday. we usually do three centres in a fortnight.
However don't discount tour ops as they often have good deals that DIY may not better.
Most resorts have an abundance of restaurants (but do check) and eating out is the norm. Restaurants range from the simple to the sophisticated. A good meal out for two in a tourist restaurant can be had for a tenner or so.
As for elephant rides most resorts provide this facility. But if you wish you could go to some of the larger elephant camps in the Northern Thailand
