We are going on our 4th Carnival Cruise in Nov. We really like Carnival, we took the whole family (DH's parents, son, wife and 2 kids) last Oct. on the Conquest. Everyone had a great time.
On a 7 day cruise there are 2 formal nights, but you don't have to go to the main dining room if you don't want to. But you also don't have to wear a gown. MIL just wore a dressy suit, I have worn just a dressy blouse over pants. Your husband can just wear a suit or even a sports coat. We love eating in the dining room and wouldn't miss it, but I have talked to people who never eat in the dining room and still enjoy their cruise.
We have looked at other cruise lines but I can get a balcony cabin on Carnival for what some lines charge for an inside. We did an inside cabin on our second cruise and we were upgraded to an ocean view, but it was basicly an inside cabin with a window that you had to crawl on the bed to look out. I prefer a cabin with a sofa in it and you need ocean view or balcony for that. I found out on the second cruise that I really like having a balcony.
Plus the money you save on the fare you can use for excursions. For two people it is really best to book with the cruise line, we did it on our first two cruises and it really helped us "learn the ropes" and we did our own bookings for the whole family. I did a lot of research and with 8 people we saved money, for 2 people the savings isn't that much, unless you are into scuba diving or swimming with dolphins.
Whatever cruise you choose I am sure you will have a great time. If you go expecting to have fun, than you will.