With some help from Sam, we cut plywood sheets to put between the mattress and the box spring which we believe should keep the weight properly distributed even if the mattress decides to deflate when I sit on it. All we needed to do was to wait for the new replacement box spring section to arrive from the factory.
When Gretchen spoke to the Sleep Number representative on the phone, the person asked her "When you stand at the foot of the bed, which side of the bed has the problem." Gretchen replied, "When I stand at the foot of the bed and face the head of the bed, the bad section is on the left-hand side."
We waited two weeks for the new box spring section to arrive and when the delivery folks brought it upstairs, it was for the wrong side of the bed, because the side of the bed that Gretchen had correctly described is called the "Right Side" of the bed and the person on the phone had ordered a "Left Side" of the bed, because when you face the head of the bed from the foot of the bed -- well, you get the picture.
The delivery folks (who were quite competent) took the wrong section of bed away and placed an order for us for the correct section of bed. After another two weeks and a day, the correct section arrived and was installed by a different pair of delivery folks.
Tonight, we will see how it works, a month after initially reporting the problem.