Use verbal discussions to build the relationship with your client and gain mutual understanding. However, don't use verbal discussions as the source for a binding contract. Instead, through verbal and written discussion, work out a mutually satisfactory, written Master Services Agreement (MSA).
Now for each project, or for each set of new scope, create a Statement Of Work. The Statement of Work is contract that refers back to the MSA and focuses on defining the scope of work and any project specifics not covered in the MSA.
The SOW should feel like a formalization of what will meet the client's need based on your problem-solving discussions with them. It shouldn't feel very legally-oriented (even though it is a legal document), since the MSA focused on the business legalities.