I have been using an unused saddle pad for some time because I don't have a proper kneeler, I just fold it in half and put it on the floor. It's thick enough and soft, but even then after a while my lower back starts to hurt, even if I have my torso straight. My knees are fine, it's just the middle to lower back. I don't know if this would happen just the same in a kneeler with a good cushion, because I have never been in one for any substantial period of time since I have nowhere to go to Mass here.