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.
Consumers should also be aware that a memory foam mattress isn't all memory foam. Usually, there are at least two layers, and the top or comfort layer is memory foam. Beneath that, there's a support layer that typically has some spring to it. For example, some 12 mattresses may have only 2 of memory foam.