woocommerce quantity must be identical to previous quantity

Am really struggling with what should / could be simple – if i sell 10 place settings, i need to add 10 matching place kits lesons kits to my basket, (no, not free :)) if I sell 13 i need 13 place kits added to the basket etc, there is always ever only two items in my basket – so by default if the customer chooses 13 place-settings, I have to have 13 corresponding kits in the basket already (thanks to some wonderful for that snippet) now i just need the quantities to match??? Please help me