There's an "easy" (I think it's called Novice) difficulty setting in all three Stalker games, indeed.
However, in Stalker you don't start with good gear, this needs to be taken into consideration. It takes a while to find good weapons, providing better aim / precision. It's at the start, with awful pistols, that regardless of difficulty you might still have a hard time. But generally-speaking, if the main goal is to play to essentially explore and look at the scenery because it's set around the exclusion zone and you're just curious about that aspect then I'd say it's not going to be much of a problem. If I recall correctly, the easiest settings decreases aim accuracy on enemies (well, humans that is; not sure on what it does to the critters in the wild, maybe less health points and aggressiveness, but don't quote me on that one).
I still feel hesitant in basically saying all this because Stalker is a kind of game that can be different enough from one session to another, from one player to another. But playing the game on the easiest setting would definitely help alleviate anything else the game has to offer as a challenge (or an actual imbalance, making it "tough" but for wrong reasons). So the gist is that it should be "ok" on the easiest setting, but do expect a rather slow start.