Blender: How do I keep sim rig on ground level?

I've just started making animations and can't for the life of me find an answer anywhere so I decided to just ask myself on here. How do I lock my sim rig from lifting off the ground and moving axis when doing literally anything? I'm trying to make my sim fall on their knees while their feet stays at the same location but they just end up moving off the ground and I have to locate them back to the original position.

Also I've avoided making walking animations because of this too. My sims just looks like they're gliding or moon walking forward. I've seen a tutorial on blender but it wasn't with a sim rig so they were able to lock the rig position in place while making the walking animation and then just moving the rig forward and it looks great. Any help would be appreciated.