cc bed mattress moves along with bedsheets animation

I assume you tried manually editing weights after transferring them? Otherwise the sum of weights would equal 1. When you do this, the rig needs to be selected in the armature, otherwise weights wont auto normalize.
Separate your mesh into blanket, pillow and mattress, naming them accordingly. Do the same with the reference, naming them ref_blanket, etc. Transfer weights from ref_blanket to blanket and ref_pillows to pillows. The mattress is assigned to one bone, so you dont need to transfer, just assign it manually. Then everything should behave as intended.