I found some light-weight denim stretch jeans at Walmart that worked out great. I also took a 2nd pair of regular jeans and was very glad I had them, especially for hiking. I took too much in the way of evening clothes. I thought we were going to have 2 informal (semi formal) nights onboard ship, but we only had one.
As others have suggested, don't overpack, and focus on the casual. Take what you need for formal and semi-formal nights, but also remember that a number of items can serve double-duty. E.g., By accessorizing differently (different jewelry, perhaps a shawl of a different color), a nice black dress can easily be worn two nights. Also limit the shoes you take. Shoes are heavy and take up a lot of luggage space. I took one pair of dressy black shoes, 2 pair of tennies, and one pair of casual loafers. That proved to be plenty.
Have a wonderful trip!