Regarding Domestic Cohabition

I am a married man.i want to marry one girl and I don't want to leave my 1st wife too.My wife has no problem if that girl stays with us as my second wife, as she is my wife's friend, just like her younger sister.but as polygamy is not allowed in India, how can we proceed ahead with it? We are staying in Gujrat.I am basically from Tamil Nadu and the second girl is from South America. We came to know that there are 3ways for making it possible.Please tell what's the best and easiest way which will not put us in trouble in the future , Following options we came to know about:- Option 1- Divorce 1st wife and then remarry legally.But we 3 would still be staying together after marriage. Option 2- Domestic partnership As extra marital affair is now legalized in India, can we make some written document where we can write that I would be taking financial charge of that girl for life and she would be staying in our home.we both sign on that paper, as well as we make another document where my wife signs that she has no problem with the girl staying with us and I agree to the above domestic affair.Is something like this possible in India? We find it as the best and easiest option. How much time would it take to prepare such a document? On what basis would the girl get an Indian visa? Option 3- I have heard that many Hindus converted into Muslim earlier, just to get polygamy done.Is it appropriate?