When I compose a song, I always do so in the key of c, for the simple reason that the key of c is always given preeminence by musical keyboard makers. In other words, I find it easier to write songs in the key of c than in any other key. Then, when I sing the song, I move the song into whatever key happens to be the most comfortable one for me to sing it in at the time. This saves me a lot if theory headaches.

On the other hand, if you, Flora, are playing a keyboard harmonica, then there might not be room on the instrument for you to move the tune into the key of c without jumping octaves.

The scale of triads should give you the note, but your own ear is your best guide.