Some suggestions…
Pollyanna May
Lavinia Kindred
Christabell Avonlea
Eulalie Winsome
Mabel Evelyn
Sybil Reverie
Enid Floralie
Sunday Rachel
Elisheva Beloved
Ophelia Prayer
Tabitha Glory
Docia Honeysuckle
Helen Zipporah
Jane Amaryllis
Clemency Adelaide
But if I were to pitch just one name to you, it would be Pollyanna! I feels like she fits the pastel, vintage, cottagecore, slightly clunky but sweet vibe you are going for!
I also love your ideas of Adella Mercy (perfection with your list!), and Agnes True!!