I like Cassia, but the meaning isn't nice. Cassandra has a much nicer meaning so I would suggest that.
Saffron - not bad
Tessa - harsh
Fleur - won't be pronounced correctly
Stella - okay
Portia - reminds me of "portly", sorry
Alice - cute
Philippa - okay
Camilla - nope!
Elspeth - harsh sounding
I would go with Cassia, Alice, Stella or Saffron. Philippa is fine too but will likely get shortened and I don't like the nicknames.
Ideas: Camille, Elsa, Philomena, Alyssia, Poppy, Ella, Bella, Astra, Sapphira, Sonia, Penelope, Persephone, Ayla, Maia, Isabella, Chloe, Annabel, Ruby, Skye, Summer, Layla.