I had a sailfin tang years ago and the personality of those guys is AWESOME. My sailfin used to eat out of my hand, and even let me pet him! I miss mine too, I'm sorry for your loss.
I have a purple tang in my tank with a regal blue tang. As far as personality goes, my purple is just as neat as my sailfin was. I have a hard time taking pictures of my tank because my rather large purple will swim up to the glass and block out my shots! He will follow me arround the tank looking at ME more than I look at him. Great fish, and if you get one smaller than your yellow and kole, there should not be any problems in a tank your size. I would be careful with the powder blue, I have heard horror stories about their aggression, but they sure are pretty fish. You could try a regal/hippo/pacific blue tang as well, they are very mellow tangs and would get along with what you have. Goofy tangs, if you ask me. I have had mine for 5 years now, and they grow very slow and just act.... well, strange. It will grab bubbles of air from the surface of the tank, swim to the bottom and let them go, and then 'chase' them back to the top. Odd fish.