Before I even read the names on your shortlist I thought of [name_f]Isabel[/name_f]! It pairs perfectly.
[name_f]Sophia[/name_f] would be my second pick.
[name_f]Ella[/name_f] and [name_f]Clara[/name_f] are nice but I don’t love them paired with [name_m]Leo[/name_m].
Some suggestions:
[name_f]Elena[/name_f], [name_f]Mia[/name_f], [name_f]Sienna[/name_f], [name_f]Nia[/name_f], [name_f]Maya[/name_f]