Ok how much coco fiber would I need
I did notice since that the picture you posted on another thread shows the substrate looking quite deep, sorry I hadn't realised. So the depth you already have looks good for burrowing. However what Aracnoenthusiast said about filling it up higher to help prevent falls still applies. My tarantula keeping guide says that the walls shouldn't be any higher than twice the leg-span of the tarantula, as a general rule for terrestrial species. So for mine I have filled the enclosure up with substrate until my T can't climb any higher up the wall than twice their own size, if that makes sense.
What is the substrate you are using - is there something else below the wood chips?
Ok so coco fiber is good, btw he is a Mexican red knee