OP:

Which cruise line? Well that depends on your budget. Care to share your budget with us, and perhaps the best line for you will be more obvious.

As others have said, cruiselines are not as formal as in the past. And those with a "formal night," require much less of the passenger than before.

For example, Seabourn just requires a jacket (no tie) on formal nights. And that is only for the main restaurant. There are three other venues to choose from that have no burdensome requirement.