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.
A plush mattress has quilting under its surface fabric and is softer than firm and extra-firm alternatives. For many, plush is a happy medium between a firm and a pillow top mattress. Those who frequently sleep on their sides and back might prefer the extra cushioning that a plush mattress affords, without compromising the support and durability of the inner coils and support structure.