How to display an add to cart button for each product displayed in my views grid?
Surely your issue was solved a long time ago, but this could be useful for other people, so in short :


in advanced settings of the view, add a relationship Commerce Product: Referencing Node (Relate a product to the Node referencing it through field_product) with your product type
then add a Contextual filter 
(Node referencing products from field_product) Content: Nid

then you're be able to pick up Add to cart form from Add fields menu


Enjoy ;)