These are some websites you may find useful.
Tenancy Services, including a template for a house sharing agreement: Flatting ยป Tenancy Services
Citizens Advice Bureau: information on renting, flatting or boarding
Going for Good Renting: A Guide for Renting in Later Life
My Home, My Choices guides to help with housing decisions for older people:
B2 – Sharing Your Home (goodhomes.co.nz)
B47 – Going Flatting with Others (goodhomes.co.nz)