My garden has grass - wild flowers and wild grasses and I can walk in it. Even barefoot (not often, I'm a city boy unused to that). I sometimes walk just to pick up fruit from the couple trees here and there. I'm not even sure what the problem is that requires you concrete in garden, maybe if you need a wheelchair then yes paths might the way to go (I only assume, because I'm not in that situation). Otherwise lawn looks to me barren, a sad splotch of green nothingness. Some neighbours insist on lawns, good for them, even asked me why I don't, and I gave them the above answer. They weren't happy with it as I assume you won't be either, but here I am.

I just have some big flat rock set legs-length apart to make a path. I don't have anything against grass, but I much rather have wild flowers, vegetable and fruits growing.

You don't need to concrete the whole thing. A few paths is enough.

Does the entire surface need to be grass to be able to walk about? What about some grass pathways through a variation of shrub, trees and meadow?

Personally, my preference would be moss.