have you tried using the search box? I just did using small and large - you have added those sizing into your product title (which is good)
and the search brings up all of products that meet the search word.
You might want to change the language in the search box or add a info box that suggests using the search
Additionally, you don't seem to be using tags with in your products. they can also add to the search results.
These are some immediate and no cost solutions for you.
there is
https://marketplace.abantecart.com/elastic_search?keyword=search in the MP that will do what you want, you might look into it if the above is not enough for you. This is not a free solution.