note i've pretty much adapted to the idiotic greens by avoiding POIs and levelling up via mining and collecting bird nests and getting stuff from traders - so the game is not any more challenging and no need to lower the difficulty, its just forcing me to avoid questing and POIs which presumably the developers worked hard on. LOL
Don't worry later the POIs won't be a problem for you anymore. I also had my doubts whether I could still go in POIs after I met the first radioactive zombie and it killed me immediately and then again when I wanted to get my backpack.
At the latest when you have a steel armor with the appropriate mods and Pain Tolerance at 5 you are a walking tank. As long as you don't let the zombies push you into a corner they can't hurt you much anymore. Of course it also helps to invest in Heavy Amor and Healing Factor if you have points left. Then you regenerate very fast and the armor protects you even better.
I am now level 120 and equipped with a military armor with additional mods. But my chest armor is still a leather armor because I haven't found a bulletproof vest yet that could take all mods from the leather chest armor. What helps me the most in critical situations is my shotgun with a Rad Remover Mod. This is the best mod you can have as it disables the regeneration of the radioactive zombies for about 90 seconds.
I can now do level 4 trader quests without major problems. However, I have got used to some things that are helpful.
Before I go into the building then I open all exits and windows from the outside so that I always have an escape route open. As I open the doors and windows, many zombies come out of the building so I can fight them outside which is much easier than in a confined space.
When I enter the building I work room by room. Every time I enter a new room, I wait a moment to see if zombies come running and then walk back the way I came and pull them out of the building.
I don't loot anything until I'm sure I killed all the zombies in the building. So I am not in danger of being overloaded.
And I rarely go the way the developers give me with the lights. Often these dungeons are designed to trigger the zombies when you reach a certain point. With that I circumvent the problem.
For example, in Navezgane there is a mansion on top of a mountain. Below it is a laboratory with some strong zombies. If you open the door to the laboratory, the zombies all wake up at once. But if you use the exit as an entrance and sneak up on the zombies from behind, they won't wake up all at the same time and you can deal with the zombies individually.
You can also make many levels by selling things you made yourself to the trader. Parts of an iron armor or tools are available here.