Appreciate the info about a Walmart-Humana plan, had not heard of it.
Our supplemental (wifey and I are within a week of the same age) is a "Plan F" which for the two of us is a bit less than 300 bucks a month....we got familiar with that type of plan because of my parents; in their final years there were tons of procedures and hospitalizations and I never, ever wrote even one check - Plan F covers everything.
Our insurance agent, as well as a lifelong friend who's career was an underwriter, strongly suggested Plan F.