Anyone have any advice for those of you who have parents or in laws providing childcare while both parents work?

We are seriously considering having my mom help part time caring for our LO and have her attend daycare for the other half of the time.

Our relationship has been a little rocky recently and she isn't in the greatest of health, but is a very loving and nurturing woman who would give my child a lot of love while I have to be at work. But I know we would need some kind of official agreement in place because there is a child and lots of financial concerns involved and I don't want there to be misunderstandings or hurt feelings if possible.

If any of you have an arrangement like this, I would love to hear your experiences. Thanks!