Warmbac 6mm knee pads
Well thought-out, high quality with thinner neoprene straps for comfort, and a fairly durable 6mm fabric across the front. Any* knee protection makes sense from very early in a caver's career... This solid and budget product allows this!
If you wear two sets of knee pads, one inside and one outside of the oversuit, these are probably most suitable for those on the inside.