I like either a really small gents folder like my new Fenix or a small fixed blade
like the Busse skelly assualt Shaker. The skeleton handle makes it nice and slim and with the right sheath preferably with a clip on the sheath like you would have on a folder it fits in the pocket just like a folder. You don't have to open it though and it is stronger.

Here is a closed pic of the Fenix with the Keeper for size comparison.

I am really happy with the Fenix knife ,it is made of the same decent stainless as the Byrd knives and has a nice G10 handle. Solid lock up and the same black coating as the lights. I also am a fan of the spear point blade shown in the next photo.

There is a clip but the knife is small enough to just drop in a pocket. Usually t ends up in my Moms purse as she has taken a liking to it.