You'll be applyinf or a spouse visa. A letter from yourself explaining the situation, a letter from your parents explaining you will stay with them, a letter from your company stating your employment and evidence of you financial ability to support your family (including bank statements and wage slips for the last 6 months) without recourse to public funds are the primary documentation you will require.
The fact you haven't paid NI contributions will not affect your visa process at all, and is not something that the application will look into.
You will have to provide photocopies of your son and your own passport and a birth certificate of your son showing that your wife is his mother would help as well.