That's what I want to change to cause the coco is too dusty even with keeping humidity up. And expensive. Im just worried about what to purchase to make sure its safe. I hear people buying from Lowes. What brand? The no float? I know it doesnt need pesticides etc. Need alot of substrate for the lesser price.
I use about 4 inches of very damp/wet coco coir that has been packed so tightly that it is almost solid, with about the same number of inches of fir bark on top. If you are getting dust from your coco coir, it is too dry and needs to be seriously dampened (not just the surface). The coco coir acts as a reservoir for the moisture needed to keep your humidity up and steady.
Personally, I don't care for the smell of cypress mulch, but its your call what to put on top. Some people only use the bark or mulch, but you still need to keep at least the bottom inch or two of it wet enough that you can feel it if you push your finger down into the substrate... see it stuck to your finger when you pull it out.
Getting from a garden center/home improvement place is cheaper than from a pet place.
As Tom said, be sure to read all the info on the labels. There could be something in the small print that you don't want near your tortoise even if the larger print says its "Organic" or whatever. Your tortoise will be stuck with it 24/7, so its up to you to make sure its not going to make him sick.