One idea would be to have low-growing carpeters that don't mind the occasional foot on them. Plants such as thyme or chamomile would also release scent

I have pansies that have self seeded between paving slabs. When there are too many I just weed a few out. They look very pretty. I've also seen violets between slabs.
I have thyme between slabs on a path too. The woolly one is doing best. Silver edged leaf one and lemon scented one both died off - maybe they took being walked on less well.

There's a company in the US called "Stepables" which sells plants that you can step on. Have a look at their website. It's been redesigned since I first found it - I think the plant selector has been taken off, but it's still worth looking at for ideas.

Mossy saxifrages self seed readily in our garden and many appear in the cracks between slabs. A 'walkable' plant is Azorella trifolia (or something like that). It is a green plant and as hard as nails.