Go to your local garden supply store and ask for certified organic compost/soil.
And if they don’t have any, ask them to order some, because a garden supply store without it isn’t worth the name.
The regular bagged soils contain synthetic nitrogen and all kinds of other garbage including plastic pellets.
If it doesn’t smell like a forest then it isn’t what you want.
Also drop into this thread sometimes and maybe you’ll win some seeds. 
And don’t rely on 10 weeks to get a fully mature harvest. Even for auto’s that’s very optimistic.
You’ll have something but it might not be very strong or too much of a nervous head buzz.
If you want a heavy body stone then you want to wait as long as possible to harvest,
like until the leaves are shrivelling up and your plant is almost dead.