At last found somewhere to buy hobby quantities of the stackable headers besides just the 1 x 6 and the 1 x 8 ones standard for Arduino. These are the same pin size as the Arduino ones. It’s Electron Hobbies and their stackable headers are at http://electronhobbies.com/category.php?id_category=16
And they are based in Australia so don’t have to ship from overseas !!!
Excellent.