I can totally understand how this is proving difficult!
I really like these already-listed suggestions:
Sage
[name_u]Willow[/name_u]
[name_f]Ivy[/name_f]
[name_f]Opal[/name_f]
( I LOVE [name_u]Lark[/name_u] from your previous list! )
I also like:
Lake
[name_u]Reed[/name_u] - unexpected and fresh for a girl
[name_f]Coral[/name_f]
[name_f]Maris[/name_f] - meaning of the sea
[name_u]Palmer[/name_u] - maybe shortened to Palm to fit your criteria?
[name_f]Dalis[/name_f] - taken from [name_f]Dalia[/name_f], but modified for criteria
[name_u]Hollis[/name_u] - a form of [name_u]Holly[/name_u]
[name_f]Elle[/name_f] - I associate this name with nature
[name_u]Camille[/name_u] - also has nature associations imo
[name_u]Bay[/name_u] - an oldie I’ve always liked, but sadly may be confused for BAE 
[name_f]Astrid[/name_f] - has a beautiful meaning, might not be your style