Personally, I like this cheap Amazon vest. It's mostly mesh with removable service dog patches, so it's very light. May not be the cutest thing in the world, but given that I live in a desert region of Texas, I need comfort over cute.

https://www.amazon.com/gp/product/B07FY8ZFT5/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1