6 days in Thailand, where would you recommend?

Just for context, I live in the U.K. but my job is requiring me to work out in Thailand for about 4 weeks later this year, but I have roughly 6 days off in the middle.

Years ago I did some travelling in SEA myself, Vietnam, Cambodia but never went into Thailand due to time restraints.

Just looking for some recommendations.. Include Bangkok if you think it’s the best option as I won’t have a chance to see the city at all on the days I’m working. I think I’d prefer to get out the city though, would like some sightseeing, good food and a couple nights out.
Don’t want it to be a million miles from Bangkok as it’s only Monday-Saturday I’ve got off so the less travel time the better!

Thanks

6 days in Thailand, where would you recommend?