well before you turn to much on your settings try a new Carerr with a starting Date in 43 and look how long you survive there
From 1939 til spring 41 the live of a Sub is rather easy as the technologies of he Enemy is rather poor as is the state of their crew but belive me it will and it does change and you'll be happy when you survive your patrol.
When you do survive a patrol in 43 at the reality level of 100% and you still think it's to easy then go for one of the big mods like GW or so and look which one will suit you best.