You may want to think about using a SSHD drive Vs a straight SSD if you are planing on swapping out your current HD. Seagate makes a nice one. SSHD's (hybrid drive) has both a SSD acting as a deep cache for fast access and a traditional HD for the deep storage. Which is like a Fusion drive, just managed all within the drive its self.
Your other option (while its still early here), is to add in the Apple custom SSD blade. Right now they are not available but I suspect a 3rd party will be releasing something sometime next year. Then you could create an Apple Fusion Drive setup.