I apologize for the delay in responding, and thank you for posting. Slips and falls should always be done safely, ideally with a stunt coordinator. One common trick is to cut the moment into pieces: show the foot sliding in a close-up, then cut to a wider shot where the actor falls onto a hidden pad or mat.
Rehearse slowly, keep the floor actually dry where they land, and let sound effects sell the impact. The audience fills in the rest. Our VFX, Animation and Motion forum is a good place to ask more.