I think it's probably okay to say OK in conversation as it's internationally recognised - from the American (phonetic) abbreviation of All Correct!
Would it be written as "òcaidh"? ;)
Perhaps the mentors here will correct me!
Ceart does mean correct/ right and gu leòr means plenty/ sufficient - so it's not far off.
I am personally also very pleased that Iain is okay at last!