Playing to achieve high kill streaks is usually not very helpful for you team. I think it's not very hard to have long streaks when you are camping on a higher roof in the background.
You see that often in coop and the result is that the player team has issues gaining ground.
I don't play for high streaks but I try to not die often, even though I tend to play aggressive. I often have a Vest-II on me and 2 in my backpack. Once a vest has a hole, I swap it instantly. When all of my vest have 1 hole each, I swap them through until each has 2 holes or if I am near an armory I buy new ones by avoid to have more than 1 hole respectively. This can be costly but I am also a looter so it's not a problem to compensate the RP I spent on vests.
anyway, welcome to the community sivistojko!