Hi Tony
There are threads on spare wheels, what will and won't work etc, search the various year range sections.
I recently got a 2018 and have put a spacesaver spare in it for various reasons.
First double check what size wheel/tyre combo it should use. I eventually found that my 2018 should use a T135/80-D15 , some other sizes have been used in different versions. I suspect your 2016 will be the same but you need to check. Late Mk3 cars (2019?) actually had the boot floor altered so it won't take a spare, but that's not a problem for you. I found a handful of this size wheel on fleabay, typically around £40ish for something tidy.
Some people have used spares from other cars but you need to check that the centre spigot location diameter is correct, they vary (plus the stud spacing and possibly offset).
You'll need a hold-down bolt of some description to retain it in the well. I picked up a brand new polystyrene insert for a 15" wheel with a jack and tools from fleabay, it wasn't for a Jazz but it worked although I altered the jack top to suit the Jazz jacking points so I wouldn't recommend the version I used, but you can find stuff to suit.
Then you need to rig up some sort of support for the boot floor mat, it isn't stiff enough unless supported from below. People have devised different solutions, I made a plywood "wedge" arrangement with a hinged lid to sit on top of the spare wheel and support the floor mat, but it can be a bit of a fiddly project.
