Hi tbonecopper,
Thanks for the update … I appreciate it.
I’m glad that you were able to resolve both your mattress and bed issues. I think the issues you had with your Ikea base turned out to be a blessing in disguise because as you mentioned some manufacturers require 5 (queen) or 6 (king size) support legs to the floor to meet their warranty criteria. Other manufacturers don’t have the same requirement which is why it can be so important to make sure a foundation matches the warranty criteria. With the Sherwood warranty you would probably have been OK since your mattress had at least 5 equally spaced cross slats with a steel center beam but it seems that it somehow wasn’t going together right. Regardless of whether it’s part of the warranty criteria though a center support leg can be a good idea.
Post #7 here and the other posts and sources of information about sheets may be helpful 
It sounds like you did very well in the end and and it’s great to see you’re happy with your new sleeping system.
Phoenix