I'm not convinced by Arabella and Isadora. They're both great names but they seem too similar, even though they're really not. I think it's because they could easily end up being know as Bella and Izzy and then you've pretty much just got Isabella!
Love pp suggestions of Jessamine and Calantha (never even heard Calantha before but it's gorgeous). Also think Felicity and Matilda are good choices.
Other ideas:
Amberley, Beatrice, Cassandra, Calliope, Clarissa, Cordelia, Catriona, Eloise, Francesca, Florence, Fenella, Georgina, Gabriella, Genevieve, Henrietta, Imogen, Imelda, Joanna, Jocasta, Josephine, Katherine, Lilianna, Lucinda, Lorelai, Larissa, Miranda, Madeleine, Melisande, Millicent, Natasha, Natalie, Persephone, Phillipa, Rhiannon, Rebecca, Rosemary, Rosalind, Rosanna, Saskia, Samara, Saffron, Tamara, Victoria, Vanessa, Verity, Xanthe, Zara