I gave up the dress routine awhile ago although I still have two that I may take for a longer cruise!
I wear a very dress pair of black pants, with a long sparkly top I made. The second formal night I wear same pants and a shell/fancy jacket I bought on sale (actually the beads, decorations were falling off so because I sew they gave me a deal)!
I've never felt out of place or underdressed because you see all kinds of different types of dresses, jumpsuits, cocktail dresses, pants suits, you name it, you'll see it.
Shop your usual stores and you'll find something!