Ah, I'm forgetting that TDI and TSI are different rear suspensions, so take this as a reference point, but do your own measuring...
But here's how I settled on the AirLift 80753 (quoting myself from
VWvortex)
I've been doing lots of reading and the two main kits recommended for current and previous gen Golfs are
Air Lift 80753
Firestone 4176
There's a big difference in the bag sizing though. AL is 3.44 x 8.75" and FS is 3.56 x 7"
I actually would prefer the FS setup, as I do not want any increase in height when unloaded, and the AL might do that (you're supposed to maintain 5 psi minimum to protect the bags). Also the bags supposedly work as well when simply pushing on the coils outward and don't necessarily have to touch at the top/bottom (especially in a non- heavy duty setup, ie Golfs).
BUT, it seems like the FS valves/fitting are more leak prone, especially if the install doesn't allow much air line slack. Push to connect fittings seem to be the issue.
There is also an 80777 air lift kit with 3.44 x 7" bags. I'm not sure if that would be sufficient though, as it also has one spacer/protector vs two in the 80753 setup (the FS one also has only one spacer - but I think the wider bag might help).
So I'm torn, as I do not see a clear winner here. I think the Air Lift may prove more likely to hold its air over the years, though, so I may go for one of their kits.
[Also, I believe I found the 80753 for under $80 and that also helped sway my decision ultimately.]
and:
I've crawled under the car with a tape measure and the best I can guestimate is that the sportwagen has almost 9" between the upper perch and down into the lower 'well' (perch) area. This is including about 3" of the spring sitting in the cup on the arm, if you know what I'm trying to say. I am going to try the 80753.
I ended up just using one spacer from the kit, placed at the bottom, with the fill valve going through it - I believe the spacer in this orientation would help protect the fill valve. Over 1 year and no issues - still work great.
I recommend measuring the TDI rear springs and seeing which setup matches up best. As you can see the varying sizes makes it seem like the measurements don't have to be exact for the air bags to help.
Good luck!