WooCommerce product page images

I cannot to find the answer to this questions as it seems all posts are related to developers not getting the product thumbs the same size.

My problem is that on a product page (such as the one linked to), I have several images of the same product of different size. When I click on one of the thumbs belowe the main image, the main image may resize and the thumbs and subsequent text jumps up and down on he page. I find this rather annoying, so I’d like to make the main image have a fixed size (or at least height) no matter the size or aspect ratio of the original image.

The page I need help with: [log in to see the link]