How to install pre finished hardwood over existing softwood floor
Laying the new floor perpendicular to the old floor will eliminate any cupping issues. Low areas can be filled with self leveling compound. I like to use a pad between flooring if a floating floor the pad gives a better feel , helps isolate small divots and is warmer due to the pads insulation value.
With all that said renting a big drum sander and refinishing is less expensive and about the same amount of work as a new floor in my opinion.
Before going forward I would watch some videos of floor refinishing and how you can make a horrible floor look better than just about any new flooring for 1/3 the price.