The best english adaptation of Wǒ hěn hǎo is I'm very good. Very is used when you are nearer to an extreme condition. Because okay means average or normal the use of very isn't appropriate. You use very to say you are farther from normal. You can say, I am very good and I am doing very poorly, Or things are very bad. Very is added when the current situation is even further from average. When using the word okay you can add just and say I'm just doing okay. Just means only or merely, it calls attention to the fact you aren't doing anything far above average, you're merely getting by and aren't doing anything special or impressive.

If someone asks how you are, it would be acceptable to say, "I'm doing very well, thank you" or "I'm doing exceptionally well!" O.K. means average, so it would not make sense to say, "I'm very average". If you are having an average day, you could say, "I'm doing fairly well. Nothing remarkable has happened".

I'm sorry. No, I'm very sorry. I was late to your party, very late to your party. I mean it's awesome. People are nice, it's good. It's very good. No, I don't need a beer. I'm okay. I'm very okay indeed. You OK? I think I'm OK. We OK!!

no one ever says that. you can say: I'm great!