I bought a PPK/s around 1969. Fiddled with it a while (yes I too got "bit"). I found a load in the Lyman manual of a 121 gr. cast bullet at 950+ so I bought a 2 cavity mold.
I had a G.I. 1911a1 and was amazed that even in factory loads the PPK kicked more than the .45!
Also the trigger was unusable in the DA mode. I was tinkering with guns at the time and tired to lighten the trigger but that resulted in light primer strikes - I returned it to the factory spec.
Heavy DA triggers are par for the course with the PP series pistol. They were the first successful DA/SA self defense and police semi auto pistol and the heavy DA trigger is just an artifact of the geometry used. There isn't really a fix for it, and as you discovered lightening the springs results in light strikes with center fire primers.
They are also a straight blow back design. The PP series were all originally designed for the 7.65 Browning / .32 ACP. The 9mm Browning / 9mm Kurz / 9mm x 17 / .380 ACP was an added after thought. In .32 ACP, they are all very pleasant pistols to shoot. However in .380 ACP, the recoil is notably sharp.
As a side note if the recoil starts to have a metallic feel to it, it's because the recoil spring is worn or weak. The trigger guard acts as a recoil buffer as it flexes slightly to absorb residual slide energy. It the square block on the end starts to impact the frame, you get that metallic feel and it's your cue to replace the recoil spring.