DSCarl, taking care of the duplicate content that the site appears to be generating is a big deal. So it definitely needs to be fixed--and that's good that you've identified it.
Ideally, you really do need to be able to canonical the sizes of the dress, for example, to the product page, which is "Green Lace Maxi Dress", assuming that you will have a unique page (along with a unique product description) written for the Green Lace Maxi Dress, which would be different than, say, a Red Lace Maxi Dress.
There are generally two ways to deal with duplicate content like this. One way is to deal with it using canonical tags. But before we had the canonical tag, we certainly did have duplicate content--and we dealt with it using the robots.txt file. You can deal with this issue with a canonical tag or robots.txt.
With the robots.txt file, you would need to identify which pages (for example by looking at your URL parameters) and stop the search engines from indexing URLs with certain parameters in them. This is pretty easy to do if you understand your site structure, your parameters in your URLs (or how you have those set up in folders in the URLs), and can add those to the robots.txt file. Using the robots.txt file sounds like it would be a cheaper option for you (rather than spending $1,000 on plugins or add-ons to your CMS).
Alternatively, the canonical tag is the way to go if you can get it to work properly. Oftentimes if it's not working properly you can contact the developer of the plugin or add-on and see if they'll help you install it or get the settings right so that it works properly on your site.
Either way, it's definitely an issue that you need to deal with, as it will have a dramatic effect on your site's rankings. The canonical tag option is probably preferred if you can get it to work properly, as all of the "link juice" and other "credit" will be passed onto the page you're canonicaling "to".