You don't need to have registered firm to get GST. Individuals can also apply just choose the option of proprietor while registering. All you need for GST is Pan Card in your name, Aadhar Card, Bank Account and address proof of principal place of business.
If you are working from home then electricity bill in your name is required. Otherwise rent agreement will do. In case house is in name of your parents etc just get a NOC on plain paper and that would be all.