It’s more than OK to use the word OK. In fact, it’s the most frequently used word in the world.
I’m a reader and in various stories, novels and essays that I’ve read, I’ve seen it spelled differently. Some writers spell it as “okay,” while others spell it as “O.K.”—but a writer friend that I respect says the correct spelling is “OK.”
I’ll continue spelling it that way if it’s OK with you.
(Image from Google)