I understand your concerns. Ours were similar when we moved here 1.5 yrs. ago. We're both on Medicare. We went to a SHINE meeting for clarity.
http://floridashine.org/ and they cleared up everything. We still have my fed gov retiree coverage & Aetna instead of a supplemental Medicare plan. Works great - we never pay co-pays, can go to any doc, & pay very little for a few meds. Coverage is nation-wide.
Good luck - be sure to check out SHINE. Their in-person counseling is cancelled due to covid but they host virtual classes now.