Gemma is expecting her second child -- gender unknown -- who will be a sibling for Magnus.
Gemma writes: "Our surname is Scottish so we liked that Magnus has a semi-Scottish connection to match but we are not wedded to that as a concept for #2. I’m not sure I’m ready for hardcore Scottish names though! We would like another name which is well established but not too common. We tend to like strong-sounding names which can be shortened to something more playful. There are quite a few boys’ names which we are considering but are struggling with girls names. I don’t like anything too flowery (with the exception of Poppy) or girly. I tend to gravitate towards girls names with the -die / -ie / -y endings, or at least names whose nicknames have that ending.
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It seems like you have a strong sense of style and a really good idea of which direction you want to go. My suggestions here are simply moulded in the same vein as your options.
Otis – If you love Otto but are facing too much opposition, how about Otto's medieval English brother Otis? It has much the same charm with a dapper style.
Remy – An alternative to Rudi without being too similar to Ru. It ranks in the top 250 in the South of England and has a rising profile.
Jago – Emulating the stylish -o ending of Otto and Milo, Jago is a cool Celtic form of James.
Rex – A great compliment to Magnus is both style -- dapper and svelte -- and in meaning -- Magnus means "great, important"; Rex means "king".
Guy – An alternative to Ted which easily stands alone. Guy is an ancient name with medieval and aristocratic heritage, much like Magnus.
Ralph – Sophisticated yet playful, Ralph has a strong style with oodles of history.
Fraser – A cool clan name which has a Scottish-vibe without being too obvious next to Magnus.
Rafferty – An Irish surname which has the same bounce and refinement as Frederick. Rafe or Raffy can be used as short forms.
Lennox – Another stylish Scottish clan name which isn't too "tartan-clad". Lenny or Lex could be used as nicknames.
Xavier – An erudite name which exudes intelligence but with a quirky charm.
Cora – Feminine but not overly girly, Cora is a name fit for a goddess in a compact package.
Penelope – If Poppy feels too popular, how about using Poppy as a nickname for Penelope? Or, of course, there is perky Penny, or even Polly or Nell to choose from.
Elodie – If Edith isn't your thing, Edie could also be used as a short form for melodic Elodie.
Eden – Another way to get to Edie is the heavenly Eden which feels sweet without being too girly.
India – Retaining the same "die" sound you like in Heidi and Edie, India, meaning "river, sea" is an ancient name, which became used as a given name in the 19th century and used for the character India Wilkes in Gone with the Wind.
Dolcie / Dulcie – Meaning "sweet", Dulcie and Dolcie are names which date back to the Middle Ages and has the 'd-ie' sound you like.
Daphne – Also sporting the same striking D sound with a light '-ie' ending, Daphne is a sweet but sturdy name with a rising following.
Adeline – A less-common alternative to Adeline with all the same elegance.
Marnie – Part Margot, part Maddy, Marnie is a playful flapper-style name which is thought to have begun as a nickname for Marina.
Pippa – Bouncy Pippa is a perfect alternative to popular Poppy.
I hope this has been of use. Best wishes for finding the perfect name.