It's an interesting niche that I think has potential, but you for sure need a lot more products, and you really have to know your niche to be able to nail down popular designs. There are MILLIONS of products on Zazzle, so the more products you have in your store, the more chance you have of being found.
I know you don't want to do personalization, but that is what Zazzle is known for, so you really do need to have customizable products, unless you have a huge off-Zazzle following that will buy your stuff regardless. The shirts don't need to be personalized, but mugs and other products should be.
Since you are aiming at crafters, maybe add some products like sketchbooks, note cards or notepads, binders, or other things that crafters might find useful? What about products specifically for pets like pet bowls and pet collars (I think Zazzle has leashes now, too?) Pet bandanas seem to be popular, and these products are easy to personalize. Since you like like to have sayings related to crafters, you could have phrases like "crafting assistant" or some other title for the pet, along with the name.
I just checked, and Zazzle even has dog beds! So take some time to explore the various pet products available, and then do research (on and off Zazzle) to see what types of designs are most popular for pet-owning crafters. If you are in Facebook groups or other groups for crafters with pets, maybe you could ask what products they need or want.
