I am the Duke of Verona (de jure), vassal of the HRE and just conquered Venice. I did it in a previous game and mucked up because it turned into a regular county (castle as main holding). Unlike that previous game however I do not have the option to turn it into a Duchy (I didn't do it that time because I wasn't sure if it was a good idea). I browsed some older topics on the subject but most of them seemed to focus on creating new vassal republics. I'm not really sure what I need to do to make the most out of this situation so any help would be appreciated.