Are you using good quality blades or the less expensive no-name type? My Olfa's last a long time. Does the mat have a self-healing surface? I don't know the "blueish" brand name, but some have very hard surfaces (June Tailor is one) that do not self-heal and are damaging to rotary cutter blades.
Wool doesn't seem to be much different than cotton, so I don't understand how flannel would be harder on the blade unless you are using the type made from synthetics. Cotton flannel is made from more loosely spun fibers than quilting cotton and so should be less damaging to a blade, not more.