Supplemental insurance coverage

Hello everybody, I know I have been dragging my feet, but I really don’t know much if anything about supplemental insurance coverage. I live in Wisconsin, receive Medicare, and can’t afford co-pays. My income is quite limited, but yet too much to receive medical assistance. Does anyone have supplemental insurance that has really low copays and not cost too much per month? Or, who can. I talk to to get the information I need to. Make a good decision on coverages?