All of these quotes are simple and touching. I hope you like them as much as I do. I found them and many more here.
Gratitude is the fairest blossom which springs from the soul.
Henry Ward Beecher
Joy is the simplest form of gratitude.
Happiness is itself a kind of gratitude.
Joseph Wood Krutch
Gratitude is the most exquisite form of courtesy.
Silent gratitude isn’t very much to anyone.