You can major in anything you want as long as you take the prerequisites that are necessary for medical school. Choose a major that you find interesting.
In my daughter’s school there were a variety of majors within the school of public health: biostats, nutritional sciences, epidemiology, etc. You can choose any of these majors while taking the classes you need.
Majoring in public health will not limit your research opportunities. Many students major in public health and are involved in all kinds of research.
You will be taking difficult classes as a premed student. This will continue into medical school. You will also be taking lots and lots of tests. Avoiding classes in order to preserve your gpa is not realistic.
My advice is to choose a major that you find interesting. Best wishes!