Just buy some of those thick, rubber washers from Builders or some rubber buffets. The best I have found so far for my PS4 is the rubber stick on feet you get with some PC cases, stuck four of them to the bottom of my PS4 and removed the rubber below the power/eject button.

My fiance's PS4 has four loose rubber grommets lifting the PS4 up, also helps keep it stable from bumps, etc. You can find grommets at Builders near the bathroom/kitchen area. RJK manufactures them in SA and they look like this:



Opening up the HDD bay and "tightening" the screw there did solve my eject issue completely, but it does not seem to work for everyone. Mine could be a combo of the rubber feet, the removal of the stock PS4 rubber foot or the screw tightening. Or just my swearing at it everytime it decided to eject my discs.