General Kindness:
* As gentle as a summer breeze.
* As warm as a sunny day.
* As sweet as honey.
* As soft as a feather.
* As comforting as a warm blanket.
Empathetic Kindness:
* As understanding as a wise old friend.
* As sympathetic as a grieving mother.
* As compassionate as a caregiver.
* As sensitive as a flower petal.
Generous Kindness:
* As giving as a philanthropist.
* As open-handed as a generous benefactor.
* As selfless as a volunteer.
* As sharing as a mother with her child.
Thoughtful Kindness:
* As considerate as a good neighbor.
* As thoughtful as a true friend.
* As attentive as a loving parent.
* As helpful as a guiding hand.
The best simile for you will depend on the context of your sentence and the specific type of kindness you want to describe.