A week in Thailand

[SlimRick]

I'm getting married in August, and for the honeymoon we thought a trip to Thailand might be fun.
The plan would be to spend a couple of nights on an island / beach villa, then a couple of nights in Bangkok, then another couple of nights on a different island.
Has anyone done anything similar, or could anyone offer advice on where we should stay?
Are there agencies that would arrange something like this, or are we better off organising the individual parts ourselves?