I am usually a size 27 in most brands, so I purchased a pair of 27's. If you do not have skinny legs, you could go up a size. Don't get me wrong, the 27's fit well in the waist/hip area, but they are a little snug in the legs. If you don't mind the snugness, stick with your usual size. They are stretchy so you can easily get your usual size or go up 1 size. They are very forgiving. (FYI: I am 5 feet 4 inches tall, about 125lbs) - the jeans bunch a bit on the bottom, but not a big deal.
As for the jean material, it is soft and plush, not thin like some jeans. Great wash and I love the zipper detail!