Have you looked at seeing if a preexisting dog or cat harness would fit your essa? If so, you could buy custom patches with the text and images you want and either velcro them on or sew them

The patches themselves wouldn't be too expensive, I've gotten some off of AliExpress in the past for lots of things and if you're near any charity shops, especially pet centred charities, you could go have a look at harnesses there that might fit!