"You're doing really good for yourself." is ungrammatical, and it's ambiguous. It could mean that someone is "doing himself some good", as in eating well, upgrading his education, etc.
Or, it could be that "good" was used where "well" should have been used."You're doing really well for yourself." is a compliment. It tells someone you think they are successful in life.
It's up to you to decide which is correct for the context you took the sentence from.
Whatever the context, the meaning has nothing to do with "doing yourself". This is a slang phrase for masturbation. :/
- For Teachers