Next step in Seller Financing

[Andrew Cosme]

I met with a seller, and we have verbally come to an agreement on purchase price, interest rate, down payment, term length and monthly payment. What is my next step in the process to legalize it? Would this be a letter of intent or promissory note? If so, is this something I can get a template of online or do I need to seek one of these documents from an attorney to then present back to attorney signed by both parties to then draft a formal contract? Thank you in advance for your help.