My favorite yeast for the style (and for many other ales) is Wyeast 1007. Ferment at 58 - 62f and you will get a very clean and crisp beer.I’m gonna’ have to try OK-II on my next Kolsch. I used the Dieter since reviews said it cleared much better than (and faster) other Kolsch yeast like WLP-029. That was what I found, especially with a dose of Biofine.
My default for Kolsch hops are Tett and Mittelfruh. I also like Pearle, but Saaz was the closest I could find most ‘noble’ in an oil or distilled format.