You'd be hard pressed to find anywhere quieter in the George Square area. There is a Wetherspoons right at the front of Queen Street station, the Camperdown Place which has step free access - but then, so does the Counting House according to the website.
It's worth taking a look at the Sir John Moore on Argyle St a short stroll from Central Station - a block away (Glasgow is built like New York, on a grid). It's big and spacious, again boasting step free access. Its likely to be quieter than the others, because it's more of a business district.
I'm guessing most folk will come into Central Station, but if you come into Queen street it's only a ten minute no traffic walk, or there's a shuttle bus between the two main stations that often takes longer than walking it.
And for carbophobics, Wetherspoons now do a Quinoa salad.🙂