To change number of products per page on archive/shop page go to Cusotmizer – WooCommerce – Archive/Shop and set Number of items
It is possible to enable user select box for archive/shop page, where can the users define number of visible products. To do it go to Cusotmizer – WooCommerce – Archive/Shop and enable “Number of items user select box”, set the “Second number” for second number in the box.