WooCommerce add price in variations

Hi all, I have a dilemma that I hope someone can help me with.

I have a jewellery website with over 20,000 products. On the single product page I will have two variations drop down boxes, one for “Chain Thickness” and one for “Chain Length” and each variation will add an additional price to the overall cost of the product.
Example, the flat price of a Necklace is ￡100, a user then chooses 24 inches from the “chain length” drop down and this adds ￡10 to the price, the user then chooses 2mm in “chain thickness” drop down and this adds ￡5 to the price, so the overall cost of the necklace is ￡115.
I don’t see the point in going back through my CSV file and adding these as variations as the variations are not products in their own right but are just merely “add ons” to the original product.
How can I achieve this?
The closest plugin I could find is woo dynamic pricing but this doesn’t seem to do what I need it to do.
Many thanks