The cheapest sleeper, and the only one available when I booked, is the Upper Berth.
It’s a clever, space-efficient arrangement. [Do I sound like a realtor?] There are two facing bench seats by day, which the Car Attendant converts to a Lower Berth for the night. They also pulls down the Upper into a full-length bed with fresh linens and duvet. I’ve been grateful for all my years practicing yoga, as climbing up/down and un/dressing require a bit of agility. I also learned why VIA urges checking all but essential on-board luggage: whatever you carry aboard shares the bed with you!
The rooms are, well, roomier…at an appopriately higher fare.