girljam - you might try to help the harmonizer out in sections by duplicating the vocal parts with a sax section or brass. This way, the artificiality of the harmonizer gets masked a bit, plus it will introduce some variation to the song. Try some close voicing å la George Shearing with the melody at top and bottom of the chord and see how that works out for you.

(If this is too tough to play, try just playing the melody and use the Melody Intelligence feature of your arranger if you use Roland - not sure what this is called on other makes, but it follows the melody around with a close voicing based on the LH chord).