The go-to resource for ferries is ferrylines.com.
When I search for ferries from Italy to Greece, it lists 26 results:
We can readily see some of them are departing from the north. Specifically, there are six lines from Venezia to Greece:
You can use their search engine for yourself to look for further alternatives and information. If you feel ...
You have few possibilities:
The most used option, the ferry: Ancona to Igoumenitsa or Patras, twice a day. I do not know if Ancona is too distant for you, but you should definitely check such ferries: they are frequent.
You may find also some ferries from Venice to Igoumenitsa and Patras, three times a week.
I cannot find a route from Genoa or France (no ...