If it's possible by the time you get to Bariloche, I'd recommend the lake trip across the border to Puerto Varas, staying overnight at the hotel in Peulla. The views of the volcanoes, Osorno and Tronador are stunning, the stay in Peulla is very nice, it's an old wooden hotel, and you might hear mountain lions roaring at night. Amazing views of the southern night sky as well.
I did the trip many years ago, in the opposite direction, so I can't help with tour agencies unfortunately.