The term you're looking for is "owner financing".
The contract of sale for the state of Washington. Should be available online. you can also have an attorney prepare everything
I would recommend a title and escrow company. There are small firms that have attorneys as title and escrow. Which county are you looking to close in?
You would be able to get it done with an attorney. But in NJ most of the trasnactions need a title company. I can refer you to the one I use from the office. One of the best I have dealt with in years.
google good attorneys that handle real estate sales in mason county or the optional route is to hire a real estate agent to handle both sides. Most real estate agents earn 3%commission for representing the seller and 3% to the buyer(you). Also do not forget commission is negiotiable and a good real estate agent knows the ins and outs and are willing to handle the full transaction for 4%. Find an eager and hungry real estate agent with atleast a couple of years under there belt.