We went on Windstar, southern Caribbean cruise about 4 yrs ago. Was wonderful. Service was absolutely excellent. Many of the staff members remembered our names after the first night. Food was very good. I like the fact that they had open seating for dinner. Ship is much smaller so we could go into more & exotic ports of call.
We're not for dressing up much either but rather for relaxation. We didn't feel that we needed to dress up that much. We just wanted to chill out and de-stress.
Downsides: No private balconies and rooms are quite small, unless you get a suite. Pool area is small, so if you want to swim, be aware that it will get crowded quickly.. but deck area is large and there are many private spots to curl up with a book. If you're into tons of activities, better to stick with a larger boat as Windstar is more for zoning out.