Wow, our tastes are so alike! I’m in the UK too and [name]Ivy[/name] is my favourite name in the world
I also love most of the names on your list! These are the ones I would remove and reasons why (bear in mind, I’m being very picky since you have such a great list!):
[name]Adelaide[/name] ([name]Ada[/name]) - I adore it, but would worry that you’d end up with the inevitable and very popular nn [name]Addie[/name], which would definitely detract from the names beauty. If you push [name]Ada[/name] as a nn though, I’m definitely on board!
[name]Eleanor[/name] ([name]Nora[/name]) - beautiful name, and beautiful nickname, but a little “boring” to me. Not as fun and energetic as [name]Ivy[/name].
[name]Gemma[/name] - my sisters name, and the name of a million girls I went to school with! I’m not sure how old you are but I’m 25 and grew up with LOTS of [name]Gemma[/name]'s, almost as many as I did [name]Sarah[/name]'s and [name]Lauren[/name]'s so it seems a little dated and overused to me now. Certainly not as fresh as your other choices.
[name]Phillipa[/name] ([name]Pippa[/name]) - I love [name]Pippa[/name] but have a feeling it’s going to become hugely popular thanks to the Middletons. And [name]Philippa[/name] seems a little formal and stuffy as a sister to [name]Ivy[/name].
[name]Rosa[/name] - this has never been my favourite (I much prefer just [name]Rose[/name], [name]Rosalia[/name], [name]Rosanna[/name] or [name]Rosaline[/name]) plus [name]Ivy[/name] and [name]Rosa[/name] may tie you in to a plant/flower theme for the future
Of the rest of your list, my favourites with [name]Ivy[/name] in order are (in brackets are their popularity ranking in the UK for 2010):
[name]Nina[/name] (235), [name]Thea[/name] (THEE-uh) (256), [name]Penelope[/name] (272), [name]Alice[/name] (43), [name]Eloise[/name] (109), [name]Ramona[/name] (1472) and [name]Paloma[/name] (1332)
[name]Alice[/name] would probably have been top of the list except that it’s super popular here in the UK, and much more popular than [name]Ivy[/name] (at 227) which puts me off. Same, to a lesser extent, goes for [name]Eloise[/name] plus I’d dread the common nn [name]Ellie[/name] with that one but [name]Lulu[/name] is adorable. I like [name]Ramona[/name] and [name]Paloma[/name] especially with the nn’s [name]Romy[/name] and [name]Lola[/name] ([name]Romy[/name] is an all time fave of mine) but they are far more unusual than [name]Ivy[/name].
[name]Nina[/name], [name]Thea[/name] and [name]Penelope[/name] seem to fall in the same sweet spot as [name]Ivy[/name] does - popular enough to sound familiar and for people to not find them strange, but not so popular that you meet lots of them everywhere!
[name]Nina[/name] and [name]Thea[/name] in particular are great matches for a sister [name]Ivy[/name] since they don’t have the name matching “ee” sound - but since my top 3 names are actually [name]Claudie[/name], [name]Ivy[/name] and [name]Penelope[/name], I really can’t talk! Ha.
I would use [name]Nina[/name] in a heartbeat if it wasn’t the name of my SO’s ex - it’s so beautiful and classic like [name]Ivy[/name], but also like [name]Ivy[/name] it has a spark and some energy. This is definitely my top pick for you.
Second pick is between [name]Thea[/name] and [name]Penelope[/name] - both have been on my own list for a long time. [name]Penelope[/name] ranks higher on my list (personally I plan on using the nn [name]Nell[/name] but [name]Penny[/name] and [name]Poppy[/name] are super cute) but [name]Thea[/name] may be a slightly better sister to [name]Ivy[/name].
Anyway I hope that helps a little, and to be honest, with the exception of [name]Gemma[/name], [name]Rosa[/name] and [name]Eleanor[/name] - your whole list excites me and I’d love to see you use any one of the other names! 