That was a quick turnaround... Soil's already delivered. Looks like a very good mix, fairly porous for good drainage - peat based with pumice... Looking like it will do my first re-potting a lot of good...
Still haven't received the rest of the seeds (the others should all be coming together), but decided to order some soil, as I don't yet have the need for large enough quantities to warrant mixing up my own. Green Dragon is the supplier, hopefully it's of good enough quality...