Needs a bit of advance preparation, but clear soup "jelled" with plain gelatin feels a bit more substantial.
You can tart it up with some seasoning - a bit of vinegar and pepper give a sort of hot-and-sour taste, and you can mix in a few low-cal oddments like chopped scallions and Chinese fungus or whatever.
The soup dieting option sounds enticing. I love hot drinks and probably get more calories from those than the soup, which might feel more satisfying.
Like the idea of adding stuff to add variety though somehow Chinese fungus' didn't grab me.
I'm sure it is much better than it sounds 