I have a recommendation. For my 2 small ones, I use Cloe's Collars. But the key is to get them done WITHOUT the thick canvas backing, get the fabric collar only - it's super lightweight but very sturdy too. Then you could get a break-away buckle. You may want to message her / contact her to see if she still makes the thin collars like this, as she did for me. I get the 3/8" width which is for XS/S dog/cat collars. I absolutely *love* this thin/light style!
Cloe's Collars
This is Marcel's collar, so you can see how thin it is: