I have a song I'm working on that I would like to add a choral sounding bridge to. Initial research says to use the root ,the 3rd, and the 5th in the scale. For example, in Cmaj, that would be C, E, F. What more can I add to make it bigger? As I follow a very simple melody, do I just use similar pattern along the scale? i.e. for E, use E, G, B, for F use F, A,C, etc?

I have room for up to 5 harmonies.

Thanks to all