Used to have an Outback. Not sure on the seats in my Mazda, but I do sit on a towel because after an hour they get pretty dam uncomfortable. I will change seat position sometimes during the drive.
Have you fiddled with the lumbar support? Also make sure the seat bottom is angled to match the angle of your legs roughly so your weight is (mostly) spread across your butt + legs and not just the back of your butt.