I would urge you to use the correct form, which is the subjunctive (a way of using a hypothetical thought). Using a grammatically incorrect sentence, when you know it to wrong, would be going against your goal of trying to learn the language. The reason people use "was" is because, in normal convention, the grammatically correct form of I+be is "I was". But, since the speaker is using a hypothetical situation to express their thoughts, the person says "I were". By doing this, it is clear to the listener that the speaker is commenting on a non-real thought/event, and is merely giving advice. I know some non-English teachers who would notice the incorrect form immediately. So, rather than take a chance of people mistaking you for not understanding how the language works, it's better to use the correct form - even if native speakers don't. In my opinion, non-native speakers who speak better English than native speakers are a refreshing change and should be highly respected for their dedicated studies. Good luck and keep up the great work!! :D

"If I was you." would usually be heard in normal conversational English. Grammatically, however, it is wrong. It's just that nobody much cares anymore. The correct form is "If I were you." It is subjunctive - supposing the impossible (I can't be you). But go ahead and use the first one, if you like. Nobody but an English teach will notice anymore.

I am a learner of English. I have learnt "If I WERE you, I WOULD ...." which indicates the situation is hypothetical and not real.