Question about MTB shoes?

I recently purchased some shimano shoes and clip in pedals. The problem is is that I had surgery years ago on my ankle that has caused reoccurring problems. I was hoping that being clipped in would bother my ankle but it does. My question is what kind of shoes (that don't clip in) would be best for mountain biking. When riding in the past, I felt that my feet would slip off of the pedals easily if I went through a creek. Any suggestions would be great. Thanks in advance.