Joss
Carissa
Wynne
Neve
Stella
Alma
Esther
Esme
Zoey
Lucy
Vivian
Delta
Faith
Celia
Maris
Jada
Ivy
Pearl
Viola
Zora
Ione
Clio
Edit: Just saw Lucy and Ivy were already on your list. I think they do share a lot with Sylvie! Other very similar names:
Amalie
Cecily
Callie
Clytie
Elodie
Jovie
Rosalie
Devony
Verity
Solvey (too close? Norwegian name meaning ‘strength of the sun’)