I think I'm looking at original floorboards, rotting underlayment on top of those, a delightful assortment of other boards on top of that, then Pergo flooring.

I'm unsure of the best way to proceed. My gut says to pull up the top layer of boards to remove that underlayment, but then I worry that that turns into ripping up the whole floor.

(Left Side cabinet)

(Right side wall)