Hi lastminute,
“Wallhugger” is the trademarked name Leggett and Platt uses for their design of the adjustable bed sliding back slightly toward the head when the head section is raised. “Wall-Snugger” is the term that Reverie uses for the same type of function.
Congratulations on your new adjustable bed base and mattress. :cheer: You certainly made a good quality choice with the all-latex mattress. SleepEZ uses their decades-long experience of helping consumers with latex configurations for different needs, sleeping styles, BMI and somatotypes to provide their best suggestion for a product that will hopefully have the best chance for success. While there are general guidelines that are helpful that they use for recommendations, unfortunately there is no one algorithm to predict the “perfect” mattress. At least not yet! 
Post #7 here and the links it contains provides information about quite a few different types of sheets and retailers selling them, but I don’t have anything specifically listed about split queen items. While an “odd size”, split queens are commonly ordered in adjustable beds. I did a quick search and came up with quite a few options, with Advance Bedding offering many different styles at the top of the list.
I hope that helps.
Phoenix