Maybe we can simplify it one more step? Something like this:
Constraining Terrain (a room with no exit, backed up against a cliff, a narrow hallway or tunnel, sucking mud, etc):constraining terrain limits your ability to move rapidly and unpredictably.
+1 or 2 Ob (GM's choice) to Attack, Basic, Special actions and Avoid.
+1 or 2 Ob to Disengage.
Slippery Terrain (ice, scree, etc.): Slippery terrain is difficult to stand on. Moving suddenly makes you fall.
No speed advantage for Stride.
Any time you roll 0 successes on an action, you fall prone.
Standing requires 3 actions, not 2.
Would work fine, although quite different from the Nowhere to Run, Nowhere to Hide rules.