it's highly recommended to do tenancy agreement to protect both side interest and to avoid any dispute later.. legally wise, you should do a tenancy agreement no matter how well u know the tenant

apart from the standard information in a Tenancy agreement:
- rental
- start date end date
- tenant & landlord particulars
- account details
- address of the unit
- payment terms
- detail inventory list
- deposits

highly recommended to also attach with:
- maintenance checklist (clearly stating the roles n responsible of landlords vs tenants)

all this to safeguard your interest

if you havent do one, pls do so asap.. the stamping fee and tax is worth paying. after all, rental increases your income, and hence better cashflow and proof to acquire more good props..