Citizen Stiletto is only 4.7mm thick.

https://preview.redd.it/l4lqz7qwi32c1.jpeg?width=628&format=pjpg&auto=webp&s=bbfbe9b76804a7f68e765f51e2e6d558c321de3d

Tissot T0634091101800 is only 5.2mm thick with a 39mm case and can be had for less than $200.

I really like my vintage seiko lord marvel, it’s the thinnest watch I own. Feels completely different then my alpinist. It’s also a high beat watch which is cool to see, the sweep is amazing on it. I picked mine up for 400$ on ebay

Care to define “slim”?

And are you okay with both quartz and mechanical suggestions?

New or are you open to an older watch?