Hi Papa Minja –
You can use almost any type of organic potting soil, or soilless media, to grow wheat grass. Just rinse and soak the seeds to initiate germination and place the pre-sprouted “berries” evenly over the top of your mix. Gently mist everything to keep it all moist and cover with a sheet of damp paper. Do NOT let the seeds dry out. In 3-4 days you can remove the paper, and Voila, you’ve got sprouted wheatgrass!
Designed to hold more moisture, Roots 707 is a great potting mix that contains a whole slew of terrific ingredients. I think it would work great for sprouting seed. Another soil that would work well is FoxFarm’s Happy Frog. It’s a well made mix that’s chock-full of earthworm castings, bat guano and composted forest humus.
As for organic compost, I like the texture and structure of the Garden Compost by Black Gold. It’s also free of sewage sludge and biosolids, unlike most commercial composts.
Hope this helps!