Thank you, Luit. Stachys nivea is what I was thinking as well.
The second photo you show is an amazing plant! I've had mine since 2003 and it has remained quite small; looking at it yesterday, I see it has expanded to 3 or 4 offsets finally. It didn't even bloom this year. Too much competition in the border, I guess. I started another from seed and put it in the tufa garden, where it has remained extremely small.