Would a mattress with a fitted sheet on it be considered a ta’aroves with regards to borer? For instance, if one has a mattress with a dirty fitted sheet, and one wants to remove the dirty fitted sheet (the bad) from the mattress (the good) . Would that be allowed?
No, thy are not a taaroves, because two large items, are not considered a taaroves.
Aruch Hashulchan 319-17.