Another alternative for ground cover in between the semps can be wooly thyme which needs good drainage and is xeriscape type plant not needing as much water as the regular thyme. Stays low and good groundcover.
Arachnoid semps are so interesting but in my care they don't thrive as well as I would like. Very up and down in success. I hope yours grows well, Mick!
I guess being one of the many friendly, intelligent and personality-charged enthusiasts on the forum willing to support you in your addiction and experimentation is the best I can do for now...
But one day, I may make it to France and that's why I was asking about nurseries...thanks for sharing!