Ottoline is lovely, I pronounce it with the -leen ending. I knew an Ottilie once, it felt pretty on her but Ottoline is much more fun. She's flouncy and feminine but not girly.
Names with a similar feel:
Pauline
Minna
Philippa
Justine
Leda
Adrienne
Simone / Simona
Francisca
Roberta
Jeanette
Tamsin
Louisa