I agree Oceania is a good line
If you like no formal nights , limited smoking areas (2) good food, great crew etc...
We did the Baltic on another cruise line but they have similar tours.
They have a "roll call " on Cruise critic" you might be able to join others on private tours
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012