Maybe this tutorial is handy for you. In order to filter it material wise, you can combine this system with your footstep system if you dont want to do a linetrace per tick to just get the surface type.
Footstep system
https://forums.unrealengine.com/attachment.php?attachmentid=3582&d=1400806806
Seen here: Get surface type on terrain materials? - Blueprint Visual Scripting - Unreal Engine Forums