Hi Damien,
For your time on Samui, check out The Whitehouse in Choengmon . It is a lovely area, no girly bars and an absolute picture postcard beach. It is a smaller resort, locally run with some of the most friendly staff I have encountered.
It is certainly not THE RITZ, but it is excellent value for what you pay.
You should be able to get a bonus night deal (stay 10 pay 6) in June as it is "fringe" season and for well under half of your budget you will get one of their better rooms.
The pool and restaraunt and public areas are not huge but when we were there, in June 09, it was never busy and we always found plenty of space and a beach or pool chair was never an issue unlike some of the bigger resorts.
This place is on the best part of the beautiful beach with a good choice of eateries within walking distance. If you hire a moped or jeep, you can access the busiest part of the Island, Chaweng, within 10 minutes.