Judy W., using a capo won't really help, since you can't put it on for just one chord. I don't believe any other key would provide an easier set of chords to play -- if you find a key where that one "non-standard" chord is an easy first-position three-finger chord, you'll find that one of more of the *other* chords in the song will be a knucklebuster.

To do the song at all, you'll probably have to stick with the key-of-"C" chord shapes (with or without a capo to raise the pitch) and then decide between Gm or Bb for that one chord in question. Either one works, both are "correct," and you can make your choice either based on their repsective sounds or based on what you're better able to make your hands do.

For my money, both alternatives are easier as play as barre chords than with four fingers (i.e., either is pretty difficult to play even as a "non-barre" chord).