Hi Vonderbach I think you are quite limited as that seems to be quite an old design there so you are not using CSS layouts. In a CSS layout I think you could set a height to the images container DIV as it is the image height difference which is causing the buy button misalignment. You could manually edit the images so that they have more blank / white pixels above and below but that could be quite a tedious operation unless you can use a batch image editing program to do so. Or you could set this CSS in the CSS file...
img.prodimage{ min-height:230px; }
This will increase the image height by stretching, which will cause the small images to look pixelated though.
Hi Vonderbach If you were thinking of updating the design by the way, there are "Replacement Template" options on this page here... https://www.ecommercetemplates.com/replacement-software.asp