I have a couple that marginally could be called pocket pieces. One is the 10+1 round Taurus pt145 that I have been exceedingly happy with. However, my friend has seen poor reliability with his. I sound like a broken record when I say it is a wonder of ergonomics and compactness. Price is right too.
To find a different one that you could be pretty sure would function well out of the box, you could go with the GLOCK 36. It's a 6+1. I have actually carried it in in my pocket on a couple occasions and I was able to pull it off. But it's really more at home on a hip. It has legendary reliability, though it's my least favorite of the GLOCKs because of its snappy recoil.
There is one more I could mention which will fit in a pocket. But mine is currently not working. It's the Para Ordnance C6 light double action pistol. It's a tiny powerhouse (though heavier), but alas mine has not proven reliable to this point. Hope you find something you fall in love with.
One other thing. If you're just looking to step up in power from the 9mm, consider a .40. They have demonstrated good performance and can be had in the same sized guns as their 9mm cousins. Not real comfortable to shoot sometimes, but for a carry gun they're a good choice. In 40cal, I'd consider the Kahrs, the Kel-tec 40 if you can find one, the glocks, & the springfields. I'm sure there are other good choices I'm forgetting.