This new service looks like it might be a good option for some trips within Europe, even if it is more expensive. Although this type of service was popular in the past, the budget airlines have caused a gradual decline. Hopefully this new service is successful and will encourage other rail lines to offer this type of service......
https://www.cbc.ca/news/world/europe-night-trains-1.7392322
I'd be reluctant to use a couchette but would be willing to give this a try. Hopefully these will expand in future.