Take my gecko off paper towels?

My gecko is 14g right now, he's finally eating regularly and has good poops. He's on paper towels now. Is it okay to get some coco fiber/spagnum moss in his tank?

My first gecko was from petco and died from substrate impactation. I am just so worried my new gecko, not from petco, will eat his too.

It's hard to keep the humidity up so getting substrate in there would be great. I'm just super worried about my little guy.