I don't expect you to go my route, but I think the two knives that are the best for dress clothes are some sort of swiss army knife, and the Douk Douk.
The SAK's speak for themselves, there are many sizes to pick from. As for the Douk Douk, well its the coolest knife I own, not my favorite, but the "coolest"
The Douk Douk is a nice carry size, and its thin, real thin, like metal gum (a few sticks). And the Douk Douk is robust, surprisingly robust. The only down side to it is its not in my opinion a good 4 season outdoor knife. It has a heavy back spring, and cold, wet, numb hands don't mix with the Douk Douk...but inside or for the summer? Classy and awesome.
And I have to also add the Opinel. I think my favorite folding knife period. Once you sand the handle down it becomes very pocket friendly, and again many sizes to pick from. for dress clothes, maybe a #7?