Ideas for 10 day/2 Wk Break Beginning of Dec: Thailand or ??

[limpsfield]

I'd like to get away from the second week of December and back for Christmas.

I have done a few road trips/city breaks over recent years but it's been a while since I have had a sit on my backside and read a few books type holiday.

A quick click around last week saw Thailand come up quite a lot - Koh Samui looks nice, never been there.

For reference I'd like a nice hotel, pool, beach.
Good weather, not scorchio
My budget is around £2.5k I think.
I'm going to be a solo traveller, in my 50s.

Mainly plan on sitting on my arse, but having some other stuff to do would be useful too.

Like I say, it's been a while since I have done an actual relaxing holiday, open to any suggestions.

Thanks