I think we'll be decamping to somewhere with a beach after a few days as we're taking the kids
Any recommendations will be grately recieved!
Depends how easy it will be for you to travel, and what you're looking for. A few opinionated observations would be:
Pattaya - bus ride, built up, touristy, partially seedy. Quite expensive.
Koh Si Chang - bus and ferry, quieter, possibly expensive as close to Bangkok
Prachuap Khiri Khan - long bus ride, much less developed, not too touristy
Chaam - long bus ride, somewhat developed, somewhat touristy, but cheaper.
Hua Hin - longer bus ride, developed, popular with expats. Prices reflect this.
Koh Samui - overnight bus and ferry or flight, generally very developed but quiet places can be found, touristy but easy travel and good for families. Full range of prices.
Koh Pha Ngan - overnight bus and ferry, developing but lots of unspoilt beaches, nice mix of chilled backpackers and travelling families. Avoid Haad Rin during the Full Moon Party time. North and west coasts highly recommended. Full range of prices.
Phuket - overnight bus or flight, some areas like Patong exceptionally seedy, outlying islands can be lovely. Quite expensive.
Koh Phi Phi - ferry from Krabi or Phuket. Touristy but pretty with some great scenery and boat trips. Quite expensive.
Krabi - overnight bus or flight, big area, Ao Nang is fairly developed, but nearby beaches are quiet and nice. West Railay is highly recommended but remote and expensive. Some cheaper resorts.
Koh Lanta - overnight bus or flight and bus, developed at the north like Samui, but chilled in the south like Koh Pha Ngan. Full range of prices.
So now I'm coming across like the Tourist Board of Thailand. So just ask if you want me to add more details on anywhere :-)