I've been seven times, but not for a while, the last trip happening in 2012. If YT can be relied on, it hasn't changed much. I love Thailand. Started going in 1987 and though what Thailand was in those days is gone forever, you can still have plenty of fun. Recommendations for specific places are fairly useless. Management and girls change so fast. Best approach is to keep a light fun attitude. Be respectful, don't be too cheap. Your money still goes a long way, be a bit generous to the girl who takes your fancy and you'll find you will have lots more fun. Same goes for everyday people you meet, the bellhop, you fave food stand person...be kind and the Thais will reward you amply. Especially if you make the effort to learn just a little bit about the language and try to say a few words.
Be sure to go to a soapy. They exist outside Thailand, but not the same experience. Didn't notice how long you are going for, but different itineraries allow for different degrees of fun. I had so many adventures there and love the place. Have fun.