The size of the IC isn't your problem, the NRF IC's are the same size as the one you just posted, you still have other components that have to be used so the PCB it's mounted to though, You're probably not going to want to use standard PCB material it'll be too thick, so you'll have to find thin copper clad PCB, I just actually picked some up at electronics goldmine but it was a clearance item so you may have trouble finding it.
Are you capable of dealing with making your own custom PCB this small? It would really have helped with suggestion devices if you would actually TELL us what you're trying to do, you're making it impossible to help because you're failing to specify the dimension it HAS to be. 'as thin as possible' isn't a number. 'small' is not a value you can engineer for. What exact physical space must the device fit into?