The solution was given many answers up, but not well stated-
1555 TGV Paris to Stuttgart (the Munich train is now extended back to Stuttgart)- arrive 1904. That train starts at 40 Euro each.
For more time in Stuttgart leave Paris 2 hours earlier .
(You can of course still do Paris to Munich (the route I know), dinner in a Bavarian Bierkeller then join the sleeper there (man in Seat 61 recommends the Augustine Bierkeller but plenty of others).
2029 NightJet sleeper train, arrive Venice 0834. Fares from 90 Euro each. Light breakfast included in the train fare.
Probably doesn't save much in hotel costs, but you won't get much more sightseeing time by taking a similarly timed flight from Paris to Venice, and far kinder for the environment.
Demand is outstripping supply for the sleepers showing that Europeans at least welcome the return of such trains, even if users of this forum are rather more circumspect about them.