This is a bit embarrassing… I need some options for fonts that include native circular enclosures. A while back there was a discussion of fonts that have enclosures built into them. There were several good options suggested… one of which I contributed… and for the life of me, I can’t find the thread!
You could also use any font that defines the Enclosed Alphanumerics region of Unicode. Most fonts that render these are sans-serif; Quivira is the only serif option I can find. It also has some options for multiple characters enclosed in a circle or ellipse in the Private Use Area.