The best driftwood, in my opinion, is Malaysian. Grapewood is notorious for fungus, with a possibility of toxic fungus. Mopani is known for fungus also, but less so on the toxic side.
Natural rocks can be used provided they do not dissolve in water, for example limestone. Calcerous rocks will affect the water parameters (GH, KH, pH).
A natural cover for fish are floating plants.
Amazon Frogbit,
Water Sprite, Dwarf Water Lettuce, etc.
You need to return that Pleco. Growing up in too small of an environment has serious negative repercussions like stunting and poor health. If you got him at Petsmart you have a 14 return window for a full refund.