I like [name_f]Isabelle[/name_f] better, I think. Here are some thoughts I had for middles, (starred ones aren’t floral):
[name_f]Isabelle[/name_f] [name_f]Anemone[/name_f]
[name_f]Isabelle[/name_f] [name_f]Blossom[/name_f]
[name_f]Isabelle[/name_f] [name_f]Bryony[/name_f]
[name_f]Isabelle[/name_f] [name_u]Briar[/name_u]*
[name_f]Isabelle[/name_f] [name_f]Calanthe[/name_f]
[name_f]Isabelle[/name_f] [name_f]Calla[/name_f]
[name_f]Isabelle[/name_f] [name_f]Camellia[/name_f]
[name_f]Isabelle[/name_f] [name_u]Camille[/name_u]*
[name_f]Isabelle[/name_f] [name_f]Celandine[/name_f]
[name_f]Isabelle[/name_f] [name_f]Cleome[/name_f]
[name_f]Isabelle[/name_f] [name_f]Dahlia[/name_f]
[name_f]Isabelle[/name_f] [name_f]Dianthe[/name_f]
[name_f]Isabelle[/name_f] [name_f]Evanthe[/name_f]
[name_f]Isabelle[/name_f] [name_f]Felicity[/name_f]*
[name_f]Isabelle[/name_f] [name_f]Flora[/name_f]
[name_f]Isabelle[/name_f] [name_f]Fioralba[/name_f]
[name_f]Isabelle[/name_f] [name_u]Fiore[/name_u]
[name_f]Isabelle[/name_f] [name_u]Floris[/name_u]
[name_f]Isabelle[/name_f] [name_f]Ione[/name_f]
[name_f]Isabelle[/name_f] [name_f]Jessamine[/name_f]
[name_f]Isabelle[/name_f] [name_f]Lacey[/name_f]*
[name_f]Isabelle[/name_f] [name_f]Lilac[/name_f]
[name_f]Isabelle[/name_f] [name_f]Linnea[/name_f]
[name_f]Isabelle[/name_f] [name_f]Marguerite[/name_f]
[name_f]Isabelle[/name_f] [name_f]Meadow[/name_f]
[name_f]Isabelle[/name_f] [name_f]Posie[/name_f]
[name_f]Isabelle[/name_f] [name_f]Rosalie[/name_f]
[name_f]Isabelle[/name_f] [name_f]Rosamund[/name_f]
[name_f]Isabelle[/name_f] [name_u]Snapdragon[/name_u] (a little wild, I know, but this is one of my favourites, so I wanted to throw it in)
[name_f]Isabelle[/name_f] [name_f]Susannah[/name_f]
[name_f]Isabelle[/name_f] [name_f]Thalette[/name_f]
[name_f]Isabelle[/name_f] [name_f]Viola[/name_f]
[name_f]Isabelle[/name_f] [name_f]Violet[/name_f]
Good luck finding names!