Instead of using "more gaily" or "most gaily," you could use:
* Comparative:
* More cheerfully
* More brightly
* With more joy
* More happily
* Superlative:
* Most cheerfully
* Most brightly
* With the most joy
* Most happily
For example, instead of "He walked gaily down the street," you could say:
* "He walked more cheerfully down the street." (Comparative)
* "She danced most joyfully of all." (Superlative)