Hi Jenny,
I don't know how good it is, but you could try
www.rocketlawyer.com. They have free legal document generator that will help you put together a services contract you can use. Make sure it has a confidentiality clause, a privacy statement, and a statement of work section as well as a payments section to outline how you expect to be paid and the terms and conditions of those payments. (When will you send invoices, when do they have to pay that invoice by, what is the penalty for late payments, what steps will you take on those that fall into default...)
Contracts are wonderful, complex, and necessary. Good luck with your!