What's the most reliable S-class you can buy?

I understand just being a Mercedes it means it won't be as cheap to maintain as a Toyota, but for some reason I suffer from migraines so bad that even an e-class or a lexus 300h isn't quiet or comfortable enough for me.

I genuinely have a lot of physical discomfort from the noise and vibrations. But I also have a limited budget, so I come here for suggestions.

Alternatively, is there a non mercedes that's ultra quiet and smooth? My budget isn't final yet but let's say it should be under 100k, ideally under 100k spent on the used car as well as repairs even after a few years (so no "buy this 10k bentley that will cost you 200k to get up and running")