I would consult an attorney. It may cost you a little bit of money. But if you don’t get it right and something goes wrong, it could cost you a lot of money. You could also consult other wellness centers in your area. They may have a contract that you could use as a template and insert your information into for an attorney to go over for you. Contracts are not trivial matters.
There is really not much you can put down on paper when recruiting independent contractors. The most important part for them to sign before coming aboard is the non-solicitation agreement. Beyond that you can add their duties requirements/assignments, working hours (schedule), payment schedule, the type of uniforms (if any) they will be required to wear while working at your location, rules of conducts with your clients/members, termination policy and also a list of the certifications and insurance which they are required have.
Maybe someone else here can provide you with some extra information and advice. I hope this helps.