Hello,
I started working on italic for Cosan
https://www.adtypo.com/fonts/cosan/ Although it's a helvetica-like font, I'd like to make italic as real as possible – that is rounded "e", elongated "f", single storey "a" and "g", etc. The problem is that the "ӕ" ligature would look exactly like "œ". I came up with such a solution, but it doesn't seem ideal, especially in a thin style looks strange. Do you have an idea?

Comments
“Neo-grotesque” describes either:
• An historical genre of mid-century modern typefaces such as Helvetica and Folio
• Any new type design in the broad grotesque style, that is clearly not quaint or a revival/renovation.
Genotype or phenotype.
So, if you are being authentic to the MCM genre, you need to have precedents, but if you are being innovative, the concerns are (1) legibility for specific language-users, and (2) harmony within your overall design.
As there are almost no instances of languages in which æ and œ both appear or have semantic significance (this issue has been discussed before at Typedrawers), I would say don’t worry if your æ may be mistaken for œ.
However, I would suggest that you first identify which languages contain æ in their alphabets and use it frequently (Danish?), and consider the work of type designers of those native languages as your benchmark.
• Futura's solution certainly works, but it doesn't make a logical sense.
• Avantgarde's solution would completely kill the letter "e" in the contrasted version.