we will be traveling from London to Berlin to Prague then to Slovenia, possibly going to Lake Bled and Ljubljana, and other likely tourist destinations in October. We would love to travel back to London via Italy, and would especially like to take a boat or ferry from the Slovenian coast to Venice. Anybody have any suggestions on how to do that?
Venezia Lines operates a seasonal tourist service running between Piran and Venice, however the departures are very limited in the off-season. As far as I can tell from their website, the final sailing of the year will be on October 7, it's also the only departure in October.
If that won't work for you, the usual way to get from Piran to Venice is to take a local bus to Trieste and then transfer to one of the many daily high-speed trains which will take you straight to Venezia S.L. From Lake Bled or Ljubljana it's even faster by land, either (from Ljubljana) bus to Trieste and then again high speed rail to Venice or (from Bled) train Bled Jezero to Nova Gorica, local bus to Gorizia Centrale and from there a direct train to Venezia S.L. You could also book a direct shuttle transfer.