I work at a nursery and we carry fertilome and Fox farm. I would highly suggest Fox Farm Ocean Forest over any other soil. It has enough food to last atleast a month.
Fertilome is fine for houseplants, Not MJ plants. FL has absolutly 0 nutrients in the soil, Is very very light, They don't add enough perlite to help with drainage. It's decent soil for the price but i'd never recommend it for MJ. But if it works for you, More power to you.
EDIT: didn;t realize you said for seeds. For seeds i've still always used FFOF but it can burn, so you could Mix FFOF 50/50 with SUPERSOIL, Which can be bought at homedepot. Like 10 bucks for a 3 cuft bag. but i personally don't thinks its necessary, I've popped hundreds if not thousands of seeds in FFOF and burnt maybe a few