The Yukon gets done every five years at the dealer, so not my concern.
I do the GTI myself every 3-5 years and use the VW pink stuff from the dealer. I can’t even remember, but think it might come pre-mixed.
I have the de-ionized water for my dirt bike. Coolant comes in a one-liter jug, and I top it up with another liter or so of water. The jug and a half of de-ionized water I’ve got in the garage should last me a lifetime.
Edit: Alright, so I just looked at my leftover jug of VW coolant in the garage. It doesn’t come pre-mixed, and the label says to flush the system with distilled water, then mix the coolant with more distilled water. So, yeah, probably not worth getting too hung up on the distilled vs. de-ionized thing.