So I didn't get an alignment tool with my clutch kit, does anyone know the exact width of the input shaft so I can try and find something the right size to put in there?

If you can't get a tool, there are alternatives.

You could make a wooden one to the dimensions taken from your own gearbox spigot shaft.

Alternately, if you can get your head in where the gearbox fits, you can line it up by eyesight - sighting along opposite splines and estimating the distance to the spigot bearing.

If you do the latter, don't tighten the bolts on the clutch cover assembly 'till you are happy with the results - this will allow you to lever the driven plate in whatever direction required, in order to centre it.

Regards

With the Polo I've found my index finger is pretty much perfect for aligning the clutch. But I've always done it with the engine out the car so I can see that it is central.

Alternatively have you checked to see if any sockets or extensions fit through the centre of the clutch?

So, size is important after all! - Not all fingers are the same size.

You can also centre the clutch "by eye" and then measure the distances from the outside of the clutch plate to the flywheel edge and make sure they are consistent. i've done this a few times on different cars after using an approximate sized shaft

You can also use a suitable socket and extension bar to align it sometimes.

Or a cut off bit off broom handle with tape wrapped around it...

always used my finger with no issues