Unplug the sensor from the wiring harness, and get a special O2 sensor socket from the auto parts store (some loan them out for free) and remove the old sensor from the exhaust bung. If the sensor won't budge, try more penetrating oil or attempt the removal with the engine warm (be careful not to burn yourself).
However, a mattress that is too soft is just as bad for low back pain as a mattress that is too firm. In a 2005 study, The Journal of the Canadian Chiropractic Association pointed out that in a survey, 76% of orthopedic surgeons recommended firm mattresses.
Some people use pillows between their knees or thighs to provide support for the lower back and hips. A lumbar pillow can also fill the gap between the lower back and a chair or mattress. A special neck or cervical pillow can also provide additional support while resting in a vertical position.