CSLB.ca.gov website doesn't state anything about what kind of form to use so I'd like to know if there's officially a form we must use or not.
There is not one official form that you must use -- HOWEVER, the form you use must contain all of the statutorily-required language/notice to be effective. The form must have all of the correct project, owner, claimant, and other information to be valid. The form you use must also be formatted correctly so that it complies with California law and the County Recorder's particular requirements. Levelset should be able to help you serve and record a proper mechanics lien.