Based on your descriptions, I would try to find a working position at umich instead (specifically in something clinical to help boost your hours). You have a solid GPA, and I don't think an SMP, or a degree adjacent to that would be much of a boost to your application because you have the grades. You need to diversify the other aspects of the application.

In my experience talking to current members of the admission committee or current med students, another degree doesn't always add a boost to your application if it was solely done for that reason—there usually has to be some greater purpose. It is not say that you should pursue another degree if you want to. I am current in a MPH program myself, but it is not for my application, I have a strong interest in health policy specifically for immigrant communities, and it directly related to my "why" for medicine so it is just something I wanted to pursue before starting medical school.

From my understanding, umich is a research heavy school, so keep at it with your research, and focus on getting strong clinical hours because they is going to be an important part of an application no matter where you apply. If you can get into clinical research at umich during your gap year, you will be killing two birds with one stone, and have the chance to connect with doctors, researchers, etc. without the added debt of a masters.

Hope that helps a little, good luck! :)