In no particular order
Layers of mass over a resilient material like GenieMat is extremely beneficial in a wood structure. However, additional layers of mass over existing mass without the added resilient layer will provide little benefit in isolating impact footfall noise.
Cork floors, unless incredibly thick (1” or thicker), will not significantly improve the IIC rating of a floor. Cork tests show performance of only about a third as much as rubber underlayment of the same thickness.
These types of underlayment products are often available through local flooring supply stores. The impact footfall ratings advertised by the manufacturers of these products are often well above 60 or even 70. These ratings are not realistic. Foam underlayment will help soften the cushion a little, but the material is not resilient enough and lacks density. So performance gains are often minimal, typically around 9dB in reduced sound transmission.