I brought it from an Oriental $2 dollar store. It moves from time to time, leaving residue. I have to use super glue. I guess it isn't soft & thick enough for you.
(you can see the thickness at the leftmost blue keycap with an A)
I guess you're looking for something like OXO kitchen ware rubber material? Is it too hard? And yes, shoe sole pad is very soft, or Sugru?
Sugru is harder than OXO, it sticks on keycap like permanently, unless I use a scraper like tool to remove it.
But don't try to make big rough texture like the red keycap below, it hurts my finger tips
So you can imagine how's it harder than OXO. Too hard for you, right?
I'm looking for soft AND grip. If too soft my keypress would delay a nano second.
Let's continue our creativity