"your sweetness" is correct and can be used in written English.
It is typically used as an expression of endearment for someone you love or care deeply for. For example: "I love you beyond words, your sweetness is a balm for my soul."
Your sweetness and kindness never faltered.
You shared your sweetness, sense of humor, and love with us everyday.
We will miss your love of life and fun, your humor, your sweetness and your extraordinary devotion to family.
Dearest Gabe, our 10th year without you, and yet you are always with us...your essence, your sweetness, your music, and your many gifts.
Another new song, "Honey Bee," loud and ecstatically indelicate, stomped through two chords with her usual kind of lyrics ("you've become my weakness/now I want your sweetness"), but it felt desperately relieving, the antidote to all that perfected sadness.
Sometimes I get all tangled up in correcting you and I forget to see that in your exploring and expressing, your outbursts and your gentle sweetness, your observations and your queries, all you've been teaching me.
— Robert Simonson Elizabeth Minchilli in Rome: On kicking off a meal with a scoop of savory gelato … Madame Fromage: … and if you're even more keen on throwing your sweetness-anticipating palate a curveball, how about a vinegar spritzer?
For so great is the purity of your life, so great the integrity of your customs, the sweetness of your conversation, the richness of your teaching, the brightness of your virtue, that nothing more could be desired to complete that most pleasant well-spring.
A certain pleasantly faded flower-child, hug-your-neighbor sweetness has replaced the sterner old dispensations.
Mindy, we will never forget the force of your personality, the sparkle of your eyes, the sweetness of your smile.
