re flight prices
Best thing you can do is constantly moniter prices. Are you going through Bangkok? ( from my experience only. the later you leave the higher the prices get!)

was looking for flight prices for myself just now( not for the same place!) so I put in notional dates for you. Seems that if you book directly through to Phuket it works out dearer than a flight to BKK and booking onward flight to Phuket through Bangkok airways. Cheapest booked through to Phuket I could find was £862 per adult with Thai Airways.Cheapest to BKK was £524 with Kuwait airways( through travelocity- tried expedia as well for you). Onward flights from BKK is £169 return.

The trouble with waiting is that availibility to Bangkok over the Christmas period becomes hard to come by. I've tried six weeks before Xmas and just gave up. Acommodation in Phuket also gets very booked up.

Tha Allamanda on the Laguna complex does (3starplus) suites with more than one bedroom...might be worth a look.

I've just booked fares with airasia.com Bangkok Phuket return £48 inc taxes. They have not got their December flights out yet but might be worth keeping your eyes open for prices.

Thanks for all your help! I think I will book within a few weeks