Why are you trying to sterilize your mix? and to eliminate what? germs/micro-organisms, weed seeds, insects, nutrients? (We say seed starting mix is "sterile" because it has no nutrients).
I make my own mix from mushroom compost, coconut coir (peat moss substitute), rice hulls (perlite substitute). The mushroom compost comes in a sealed bag, but I don't know that it is "sterile" depending on what you mean by that. It clearly has some mushroom spores in it, since they sprout. I don't sterilize anything. But the potting mix goes in the ground with the seedlings and is not re-used.
I agree with imafan re the oven. I did that too. The first time I tried making my own potting mix, I was using my own homemade compost. But too many creepy-crawlies came in with the compost, that I don't mind in the compost pile, but I didn't want in my house. So then I tried baking the compost in the oven. Stank the house up! I won't do that again, either. That's why I use the mushroom compost now.
And I never put garden dirt in, but you specified soil-less medium, so you weren't planning to do that.