What it sounds like you are looking for is a restricted stock purchase agreement. There are various form documents out there, but terms of these agreements are not 100% standardized. And they don't exist in a vacuum - are there articles/certificate of incorporation? Board consents? Have you dealt with IP assignments for the company in connection with the equity grant?
Obviously a lawyer can help you with these things. But there are also high-quality services like Clerky that can help you make sure these things are documented correctly, assuming your fact pattern falls within the range of options Clerky has available. For more customized or complex setups, you'd want a lawyer.
