I would pronounce
Jessamyn and
Jessamine the same. But with
Jessamyn there will be no doubt how it is pronounced.
I think a short mn sounds best, just as long as you avoid
Rose.
Jessamyn means "jasmine" and one flower is enough in a name.
Jessamyn Brooke,
Jessamyn Claire,
Jessamyn Kate,
Jessamyn Ruth etc.
"You sought a flower and found a fruit. You sought a spring and found a sea. You sought a woman and found a soul. You are disappointed."
"It does not become me to make myself smaller than I am." (
Edith Södergran 1891-1923)