This is a great idea and would LOVE to see it!
Currently wear the merchant monachal constantly because it's the closest thing to glasses that characters get to have. Glasses exist for other NPCs, so the shape of the object exists and could theoretically be added as a cosmetic for players.
Considering the general era aesthetic that the fantasy game is set in, hearing aids could be more difficult. Smaller hearing aids didn't exist back then. There were hearing horns in the 18th century, but that's not something that could practically work for the intent of the post, I don't think, as it wouldn't really stay fixed on a character and ascetically fit with the game while still allowing a character extensive movement while using it. What could be a hearing aid equivalent that could work?
An idea that comes to mind is a potential enchanted conch shell. Much like the ones you put up to your ear to 'hear the ocean', but the smaller miniature ones that could fit on/in a character's ear.
![Miniature Conch Shells]()