For the Hamburg - Stockholm train you can check Snälltåget. 

https://www.snalltaget.se/en

SJ, (Swedish railway) who had planned to start a night train between Stockholm and Hamburg from 1/9 have run into problems as Danish authorities don't give permission to the sleeper cars of the night train to pass Denmark. I also just read that there are problems with the seating cars as well but I couldn't confirm that information. Right now there will at least be a train with 3 couchette cars run by SJ between Hamburg and Stockholm. 

Thanks the Snalltaget looks good! Seems to be some availability.

There is a useful page of euronight trains which shows the availability for next 3 days without having to do multiple searches. https://www.nightjet.com/en/komfortkategorien/euronight

This whole summer-and its likely to continue that the real SLEEpers (and the /en/ has so much difficulty between sleep and couchette that it leads to hopeless confusion) have been sold out weeks ahead-seats not, on any NJ. I´ve seen one pass by a week or so ago and was not very impressed about it: it was a very old set hired by a private company hastily brought back in service-no AC etc. Only the real rail-fans connoisseurs know which train has better offer-and this will thus be sold out.

There are in WEST EUR simply not other overniters with beds/sleepers-except the Caled. Scot. IF you would like that experience ´just for to have it done´ then try POland or even better CZ/SK. There is also RegioJet , a private CZ company that has overniters to SK and PL -these trains do not take passes, but their all-in fares are mostly pretty low for what you get as combined fare. It does NOT belong to NightJet!! That is a  brandname of Oebb=austrian rails.

At the end of my coming visit to STO/SE (and to visit the ABBA musm) I had booked the new to come SJ overnite-we´ll see what comes of it. Did not yet have any notification for it.

When are you travelling @mcadv ? I guess that you’ve read about all the trouble with the SJ sleepers.