MentallyHealthySchools.org has a raft of resources, starting points, questions and ideas that can help schools develop and embed a Whole School Approach across the entire scope of the school - including governance and leadership, school culture and environment, creating a Wellbeing policy, and 1-to-1 support for staff in need.
You can get hold of the resources here - https://www.mentallyhealthyschools.org.uk/whole-school-approach/supporting-staff-wellbeing/