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.
The Sareer Matrah Pocket Memory Mattress uses a pocket spring unit to offer a consistent sleeping surface via up to 1500 individually pocketed springs that work independently from each other in accordance to your body shape and movement. The memory foam layer adds an element of comfort to the mattress.