Welcome to the forum!
What year is your Leon may I ask?
You should be able to plug and play an RNS310 if you fancied Sat Nav and a touchscreen etc or if you want to stream music via bluetooth you'll need the RNS315 then the newer RNS510 should all be plug and play on the MK2 FL which I think is 2008 onwards for the
MK2 Leon...
Most will be available on eBay one would assume just make sure you have the code with it.
Hope that helps.