Write down what you already have
An informal arrangement usually has no document behind it, which means nobody can say precisely what is included. Start by listing what the cleaner actually does, how often, and what you supply. Half an hour of observation and one conversation is enough. That list becomes the brief you issue to everyone, including the incumbent, and it is useful even if you change nothing else and it is the single most useful hour in the whole exercise.
The exercise often produces surprises. Tasks you assumed were happening are not, and tasks nobody remembers requesting have been done for years. Neither is a scandal. What the list gives you is a shared description of the service, so that any future disagreement is about whether the work was done rather than about what was supposed to be done in the first place and about who was supposed to be doing it on which day.
