IMO, I would suggest that you get what is more comfortorable for you.
I like the feel of M&P but never got to shoot one so I have no opinion on that until maybe next week when my brothers M&P comes in.
If you feel or can CCW the G27, Go for it. I find it that if you do not get what you like or want that you will not really want to carry it and what you are looking for is a second CCW. I would say take a look in to the Ruger LC9. It's pretty thin. Single stack and I think the capacity is 7 rounds? Not sure.
Kahrs are also pretty thin but some people have had problems with them from the get go but I understand that their CS isn't bad and can help. Again, This is just what I have read. There nice pistols but are very small and a lot of people don't seem to like to shoot them to often due to the grip. Look at the CW9.