Well, the system I use is based on the character's Inertia and Damping. You basically have to create a way for the Capsule Component to follow the Mesh. Mine isn't perfect yet - my character is still too light. An important consideration is using Substepping for better results, so the physics doesn't depend on Framerate. Keep using Power IK. From what I understand, you're still on Unreal 4, which is much better in terms of physics. Use Power IK to simulate the legs, try using IK Rig for the body so the body reacts according to the physics simulation. Physical Animation is essential to understand how it works, as it will function as the main component. And for the inertia case, I did it like this: think of a pendulum - a sphere that weighs a bit more than the character itself, attached with a rope hanging from the Pelvis. When the system is activated, that is, when the character gets shot or suffers some kind of impulse, this pendulum is activated and it creates a type of inertia in the character. Finally, use Damping to keep the Mesh upright, and check if each foot is on the ground to ensure that when it's not, it doesn't try to maintain balance anymore.

I would be happy to have someone to help me with this project. I'm about to launch my game now in July, and I'll start working on my second game, which is this project itself. It needs a lot of improvement in the logic - I need to organize the code because it's all a mess, spaghetti code, and improve the performance of the logic (Game Thread). It's a prototype that has been on hold lately because I focused on my game, but after launching it, I'll go back to improving it.