Plant Experts (or novices), help me out, what plant can I use?

[The Plant Lady]

Here in Minnesota we have a native moss you may already have growing in your lawn. It can be transplanted. I have a whole garden called my moss garden but is really just the walked on part of it that is moss. I love it! I also agree that the wooly thyme is probably the hardiest for a between stones application, other than the moss which surprisingly enough is drought tolerant once established.