Try an Am as your second chord, on that high note. The minors that 'normally' go with C are Am, Dm and Em. (all white notes). Try them out.

(I say 'normally' to try to fend off jaaz and blues pundits who will pop in to say "How bout B-flat7sus4th? I use it all the time.")

Me, when I play a traditional tune I might use a major chord in a certain place one time, then change to a minor on the repeat. I might use the major in one verse, then the minor in another verse. Of course, in session playing that could get a little complicated.

This is a nice song. As an American, I thought it would be a political song against monarchies, but then I discovered that Regality and Liberty are neighborhoods in old cities. Thanks for brining it to our attention.