Wow!
Germination is not really the problem with that mythic species. Try a standard mix, just keep in mind it HAS to have sharp drainage ( and later around the collar and under the cushion!). As a caryophyllaceae member, it should be able to sprout quite quickly if the temperatures are mild enough ( so I don't know if that's a good idea to sow it now, right before the winter?).
I've lost for a few years every single seedling that germinated. Tried in different soil mixes, it seems at a time there was too much "dark" stuff in the substrate, so I tried with pure sand. The plant didn't die as quick as the other, but didn't grow either. And it finally died too, after having lingered on seedling's stage 2 or 3 years...these himalayan plants
...
Good luck with that treasure, and don't forget to tell us what's going on !
