Hear me Out
I had a thought: Fitz with glasses.
In the Cities everyone's perfect blah blah blah, except that some elves don't have great vision but because of the high standards of their world they wear contact lenses in secret. Well, Fitz and Sophie are talking and he goes "I have a really big secret." Sophie's asks what's up, and Fitz tells her about secretly bad-visioned elves and she's like "Okay?" just very confused and then Fitz just takes a deep breath and blurts "I wear contacts. They aren't colored or anything, if that's something you're worried about, this is how my eyes are, but I can't see close to me and I need contacts or I'm totally blind for the first seven feet in front of me" (I latched onto far-sighted, but he could be near-sighted too if you want.) Sophie's just like "Okay, cool" and Fitz breaks down crying, and when she can finally get him calmed down enough to talk she finds out that while Della and Biana were really supportive and helpful Alden wasn't. Fitz has glasses for in Everglen and outside he had to squint and stuff until he was 10 and could use contacts, and Fitz said they were uncomfortable and he'd rather use glasses but Alden told him he had to get used to them so he didn't have to squint and gave him a weird look when he wore glasses around the house after that. Sophie keeps comforting him and naturally really wants to kill Alden but Fitz tries to justify him like "it's because of the public opinion, he just wants what's best for me' which only makes Sophie want to kill him more for not just manipulating Fitz and Biana growing up and pretty much everyone he talked to but because of the way he treated Fitz and conditioned him that that was okay.
I feel like even if you don't ship Sophitz it's still a cute idea you can use platonically because they are really good friends.
And I feel like it just works so well for their characters, especially Fitz. The Vacker legacy is all special and important, and he's been told his whole life how he has to upkeep that reputation etcetera etcetera but he knows no matter how great he is he's always failing because of his vision. And all the names people call him: Wonderboy, Golden Boy, Captain Perfect, all of it adds up on him because he really isn't perfect as much as he wants to be. He feels wrong and has a sort of imposter syndrome because he's in a family with all these important, perfect people and he'll never meet their standards and he feels so broken and useless and like he's letting his family down. And Sophie would understand that so well because she;s always felt a little broken and like an outsider, and eventually I feel they could help each other see that they're perfect as is and anyone who doesn't like it can kiss their asses.
Consider:
Subtle mentions of Fitz's glasses or contacts. Ex: (Fitz) I can't find my contacts. (Sophie, pushing glasses onto his face gently) Good thing you have these; (Fitz) Shit, I just dropped my contact. Do you think it'd be fine to rinse it really quick and just pop it back in?; A description of Sophie grabbing a book from the bedside table and being careful not to knock his glasses onto the floor.
Fitz and Keefe are really close, so maybe Keefe having known a while and saying something sweet yet teasing that makes them both blush like "It's like I said. You could wear an orange latex suit and she would still like you," and Sophie goes, "I mean, he is right for once."
Or maybe Fitz was scared to tell Keefe because he didn't know how he'd react but Sophie coaxes him into going for it and Keefe says something comforting with the right mix of cafring and joking, maybe followed by a hug because, once again, they. are. best. friends.
Maybe Keefe and Biana play around with his stuff: putting Fitz's glasses and joking about how terrible his vision is, hiding his glasses case on him, etc.
Maybe Dex making him glasses so he can wear them without anyone else knowing so he doesn't have to use the contacts as much.
The first time Sophie sees him with glasses maybe she just stares at him; maybe he catches her, or maybe she catches herself, leading to her blushing hard and looking away. Or maybe she says something about how he looks good or something that makes Fitz blush pleasedly.
Fitz not wearing glasses in the Cities but feeling comfortable enough to wear them when he's out on a date with Sophie in the Forbidden Cities or in other deemably safe places like Edaline and Grady's or the Dizznees' or Slurp and Burp, or simply when he's alone with her.
Fitz getting back the confidence to wear them around Everglen again because as long as he's been wearing them the contacts are uncomfortable to have in all the time and he wants a break from time to time and Della and Biana are so proud of him
High tension between Alden and Sophie at family events. Ex: Sophie having dinner with the Vackers one night after she finds out and she's all passive aggressive with Alden the entire night and being ready to fist-fight him at any point. Maybe she does even punch him.
Frankly, the ideas for this are limitless, but just imagine Fitz; Awkward, dork Fitzroy (because awkward Fitz is real, he literally confessed to Sophie and then had a heart attack) with glasses.
