Olivia is lovely and goes well with Jack and Penelope. If you both love it I'd look no further.
However, other suggestions (tried to avoid repeats but sorry if any slip through):
Amy, Annabelle, Alicia, Alannah, Amber, April, Aurora, Aurelia, Alexa, Amelia, Abigail, Bryony, Bianca, Bethany, Claudia, Caitlyn, Catriona, Christabel, Constance, Cassandra, Chloe, Cecily, Cecilia, Camilla, Clementine, Daisy, Delilah, Eleanor, Emily, Erica, Esther, Erin, Francesca, Florence, Georgina, Georgia, Genevieve, Hannah, Heidi, Hazel, Harmony, Isla, Johanna, Juliet, Katie, Keira, Lauren, Lara, Leah, Leona, Larissa, Miranda, Melissa, Miriam, Mia, Molly, Natalie, Natasha, Naomi, Nicole, Nicola, Paloma, Rebecca, Rhiannon, Rosalie, Saskia, Summer, Serena, Sadie, Tamsin, Tabitha, Vanessa, Violet, Vivienne, Zara