Yes we broke the U-Boat codes, but without US ships and aircraft covering the western Atlantic, we wouldn't have been able to use that information to mount an effective anti U-Boat campaign.
The Enigma encoding was actually cracked by Polish mathematicians and handed to the UK during the summer of 1939. In exchange, Poles expected the UK to join them, were they to be attacked by Germans. Unfortunately, that part of the bargain never materialised.
In WWII if you weren't victorious, you didn't survive. The governments of Hitler? Mussolini? Antonescu? Even Tiso? Japan did keep it's emperor, but he was always a figurehead and Japan's governance was heavily reformed.
Look what it took to bring Germany and its allies down down - the immense manpower and resources of the Soviets, the industrial might of the US, and the naval power and combined might of the UK and the Commonwealth. And good old General Winter working for the Soviets. And this was only 20 years after WWI's peace treaty where the factories of Germany were stripped of heavy machinery. The UK was certainly fighting for survival. When you get bankers training to use catapults seriously intending to use them (however comical the Home Guard was at times), you really are in the grip of total war, fighting for your survival.
Edit: And to more directly address a couple of those points, many countries had starvation, with vast numbers of deaths in both civilian and military populations. Britain didn't as far as I know. Children fought in many battles and the elderly and infirm too (as much as possible). These things also didn't occur in Britain, with the exception of children who lied to get into the armed forces, which at times may have been officials turning a blind eye. Perhaps it was total war in Britain, but it was certainly an easier and cheaper war than others experienced. A low grade total war?