Hi there
If you can find a suit for him on sale, that'd probably be good

Most of the people do dress up on the formal nights on a cruise. There are those people though, who get annoyed at the idea of a formal night and "having" to dress up.
When we cruised last year on a
Royal Caribbean ship, MOST people were very dressed up on the formal night, as well as the semi-formal night. A few weren't, and wore regular pants and polo shirts.
If you can't find a suit on sale for your DH, and/or he refuses to wear a suit, then how about buying a nice button down shirt for him, and a tie?? During the meal a lot of the men take their jackets off anyway.
As for cruise lines, Celebrity would be MUCH more likely to have more people dressed up for formal night, as opposed to Carnival. Nothing against Carnival, but from what I understand it is a much more casual atmosphere on board than Celebrity is.
Have fun!
