Dear Sir,
Hope you are fine and doing great. I am a Wordpress/woocommerce expert with 10 years of professional experience. I understand your requirement. I can programmatically convert your 16K simple products to variable products and create variations are required. Kindly send me a few examples on how you want to accomplish that.
I am quite sure that you'll be happy and satisfied with my work if you award me the project. I expect a positive response from you and want to make a long relationship with you.
Best Regards,
Hammad