I would like to run a game with an open world, where the party can explore unconstrained. I would like to do it in D&D 5E, but the power differences are very stark between levels. How can I make the world realistic, without scaling everything up as the players advance their levels (so, first only goblins everywhere, then suddenly orcs, etc.). On the other hand, I don't want a TPK every other session, just because the players misjudged the danger.
I am familiar with making open world campaigns in other games, where the differences in power level are less stark (and you can decrease the power gap by smart, tailored tactics and planning), but I am vexed as to achieve this in level-heavy game as D&D.