I have a recipe from my teenage years in Australia for a bar cookie called "Cherry Crunch". It includes cashews, arrowroot, cocoa and "biscuits", among other things. I know that biscuits are cookies, but have no idea what type of cookie to use. I'm assuming it would be something rather plain?
As an Australian we seem to use Arnott's Milk Arrowroot or Arnott's Milk Coffee biscuits in a lot of recipes.
I think a cookie like a hobnob would work. I put a link above if you aren't familiar with this brand. I think they would work beautifully. Otherwise I think any nice crunchy oatmeal cookie would be yummy.