I haven't done it lately, but I used to make an eco friendly potting soil for seed starting/ seedling growing:
A basic potting mix recipe goes like: compost or something organic that supplies texture and nutrients, something to keep it fluffy and moisture holding, something mineral or gritty to promote drainage, more or less thirds of each. In my quest for eco-friendly sustainable potting mix, the recipe I have come up with is mushroom compost (left over from growing mushrooms), coconut coir (outside fuzzy stuff from coconuts) instead of the peat moss that people often use, rice hulls (left over from milling rice) instead of perlite or vermiculite. All of this is agricultural by-products and all but the coconut coir can be fairly locally sourced. None of it is mined, heated to high temperatures or otherwise environmentally destructive to produce.
So I think it is very eco-friendly. It turns out that it is not as nitrogen rich and maybe generally not as nutrient rich as the Miracle Gro potting soil I used to use. So I need to supplement it a bit. Things I have used include soaked alfalfa pellets, aerated compost tea, seaweed fertilizer, etc. I still need to keep tweaking this part a bit.