Transitioning from Yearly to Month to Month lease

[George Sass]

I'm not sure if I need to include the back story or not so I'm going to. Hopefully this doesn't detract from what I am actually looking for. I had two tenants starting last November on a  year long lease. They were a couple and then they broke up about 3 months ago. Luckily for me, it was cordial and they finished out the lease with him sleeping in another room. The down part for me was that they were late every month with the rent but always came through and included the late fee without a problem. Now that it is time for the lease to be up, the woman wants to still live there but with her new boyfriend. She can't pay the rent by herself so it is a fairly uncertain situation especially with them being late every month previously. She did take care of the house though so I want to extend the lease for her. To hedge my bet, I want to switch from a year long lease to a monthly lease. Any advise or recommendations as to what I should put in my lease to make it a good month to month lease? Thank you in advance.