Add notes to client's record

I have customers who have contracted with me to perform certain tasks on a monthly basis. I would like to record the date, time, and any notes pertaining to the tasks as I perform them. That way, I can be sure the tasks were completed and if a customer asks me if a certain thing has been done, I can quickly check his record to find his answer. Is there a way to do this other than just editing the client record and adding private notes?

Thanks.

As a side note, I am using the self-hosted version 4.5.17. I saw a video about a ticketing system that is available from the left side menu, but that is missing from my install. I see no way in the admin settings panel to turn it on.

That should work…

The tickets module requires using the develop branch of the code from GitHub.