You could maybe try pearl barley to thicken it a little, I usually put it in stews, but I'm guessing it'd work in soup! It does absorb a LOT of water though!
I don't really "get" soup, it's just not a drink and not a food unless you really thicken it up

actually, I've got some leeks, potatoes and parsnips that need using, I may have to see what I can conjure up!