You can try After Beach bar. It remains open from 9 a.m. to 11 p.m. It's also a great spot to watch the fantastic sunset in the evening along with awesome dishes. It's located 4.6 km(approx.) away from Karon beach.
Well, by now you've already got great suggestions for what you asked. But if you're planning for Pattaya as well, Go to The Nashaa Club and enjoy the Vibes.