Cooler material touching the chip

Take a look at this vid: PS4 Slim Teardown - Detailed Disassembly Guide

Unless your system is giving you a heat warning I would leave it alone. You'll need to dig quite far into the system to get the logic board out to then clean and re-apply the thermal paste.

The heat sink does look like its quite massive so I doubt they would use copper given the cost difference between aluminum and copper. You also have a lot of thermal pads used in this design so you want to be careful you don't loose one and you don't want to touch them with your bare fingers as the skin oils and perspiration (or dirt) will damage them.