You might try replacing the butter with shortening, and using milk instead of buttermilk. Both the butter and buttermilk add to the richness of the biscuits, and have a tendency to make them crumbly. Also, I'm not sure what the baking soda is about, unless it's tempering the buttermilk for some reason. I can't remember a biscuit recipe that calls for both powder and soda, but then, there's a lot of voids in my remembery. It's a '60's kind of thing.
BTW, some people would give their first-born to get such flaky biscuits. LMAO