Thompsons have a ship that is adult only on certain cruises.
Although some lines don't have a ban on kids, they provide little or no facilities for them. Fred Olsen, Oceania, Azamara, Seabourn to name a few, the results being obvious......Wilba.
Plus Ocean Majesty - not a ban on kids, but no reduction in price or special facilities.
The Thomson ship Calypso is always adults only and Some of the other ships have occasional cruises that are adult only...The Calypso is a small converted car ferry around 500 passengers ...we spent two weeks on her last year sailing the Greek Islands and Black Sea and thoroughly enjoyed it...Food was good, Staff wonderful, entertainment excellent..good value for money ship, tips included and interesting itineraries.