Could try curviceps or fulvipinnis if you can find them. I don't remember which one exactly he had, but I had a friend with a pair in a tank with cardinals. They even spawned, with no harm done to the cardinals. He was British, so I don't know the exact size or dimensions of the tank, but I know it was something equivalent to our 20s.Nice tank man.
100% can up the stock agree withHybridfish7 on that with more tetras.
In my experience laetacara can be pricks to each other.
Any cichlid would really be aggressive when they breed.
Have you concidered peacock Gudeons? Peaceful, colourful and only really slightly defensive if the male is one eggs.
The bigger ones do definitely get violent on eachother though. Again I don't recall exactly which one it was... either thayeri or araguiae that is exceptionally aggressive for the genus. Whichever one it is I don't recommend it, lol. I myself have been trying to make space for dorsigera.
I still stand by the Bolivian rams though if anything. If you're willing to go outside of a biotope, which I'm assuming you are given your original inquiry about kribs, you can do anomalochromis. Those are pretty peaceful (and prolific).