... you should not go over 37 mm.
Luckily there are some quite nice Pateks to choose from:
- the 5119: gorgeous bezel, timeless roman numerals and in RG one of my favourites.
-the 6000 RG if it should be something quirky, something from the 30ies.
-or the Ellipse in RG: a groovy unisex watch, but best looking with a blue dial in YG.
That is the classicism department of Patek.
In the big watches department there is only one watch for me to advise you: the 5146 in RG.
The rest is, unfortunately, too big to be discreet.
Let us know what you went for.
Best
Moritz