Thanks, but I don’t want to change the size of the Product Images – just the Category Images. When I make the change to the Thumbnail Width in the customiser it changes both the Category Image (which is good) and the Product image (which is bad!).
They category and product images both use the same thumbnail so i think the only way would be to set the larger size for the categories and then use some CSS to reduce the size of the product images. If you want to try setting the larger size and then let me know the width you want your product images i can take a look at the CSS.
But to note its not the best way to provide optimized image sizes….