Ooh some good suggestions here, thanks!
Marianne is great but DH strongly associates it with a slightly bonkers old friend so says it's out. Might see if I can persuade him as it's a lovely name.
Have a Miranda in the close family already - shame as it's a great name. Same for Isabella.
Emmeline I really like, but DD1 is called something pretty similar.
Constance DH really likes, and I quite like, but I'm not a fan of Connie - any other nns?
Marina I like but DH just says "boats"...
Marguerite and Margot I like, but DD1's name is quite French, and we are not French so wonder if it would be odd to have two French ish names?
Saskia .. ooh. Maybe. Fits the bill definitely, but what about short forms/nicknames?
Mirren/Maren/Mara will probably get vetoed by DH for the usual "I've never heard of it, therefore it's not a name" reason 
Mirabel totally fits the bill in theory, but I find it a teeny bit too girly/princessy?