Help With SEO Product Titles Within a Single Niche

I have an ecommerce site that sells niche clothing for dolphins. While I can easily optimize the homepage for big keywords (i.e. "dolphins gifts") and category pages (i.e. "dolphin shirts"), I'm finding it nearly impossible to optimize individual listings. For example, including "Dolphin Hoodie" in the title for all of my hoodie listings seems....wrong? However, it's the only associated and appropriate keyword with any amount of search volume. More specific keywords simply don't have any traffic- for example, a dolphin shirt with an interesting design and the text "Life Is Good." Here, if I name my listing "Life Is Good Dolphin Shirt," only the dolphin shirt keyword has traffic, while the life is good bit won't ever be searched.

Is this just par for the course when working within a single niche? Is it a good ideas to include "Dolphin shirt," "Dolphin hoodie," etc. keywords for every single product listing? Or does this appear spammy and repetitive? Do I simply rely on my homepage and category pages to drive traffic?

Hopefully this makes sense. I've been struggling with this for some time. I really appreciate any and all help!