the few times i've sewn with unwashed wool they have shrunk. one was used as a batting and it pulled an entire quilt out of whack. quilts get soiled and i can't dry clean every time getting them clean. washing is the best answer.
now i preshrink it every time. and i preshrink everything that goes with it. flannel is the worst offender when it comes to shrinkage. i would never use flannel for anything without preshrinking.
EDIT: why not do a test. trace around one square. wash it in hot water. dry it in the dryer. lay it on the tracing. check the new size against the old. see if it shrinks. don't worry about the edges. they won't fray.
remember: this is a quilt. people sleep under it. it gets soiled. it needs washing. you live in a warm climate and wool is very warm. it gets body oils on it. make it as washable as possible, especially for a sick person.