Crested Gecko Substrate Help

Hey guys! I have this really great crestie named Spooby (my boyfriend named him, not I :roll: ) who we've recently decided to graduate from moss substrate to a 'living vivarium'. We're gonna have springtails and all sorts of cool stuff. We bought hydroballs for drainage and organic, fertilizer/perlite-free potting soil for substrate (which I'm currently hand-sifting to remove the sticks and whatnot) and a big, beautiful spider plant for him to jump around on.
Before we put everything in though we're gonna need a mesh layer to separate the soil and balls. I don't have time to order herp-specific mesh online as I'm leaving the state in a day or so, so I figured I'd go to Home Depot tonight and grab some there. I don't know how finely-knit the mesh has to be, though. The soil I bought is awfully fine but the holes need to be big enough for springtails to pass through I've heard. Would anyone experienced know fine/what kind of mesh I should bring home, or point me to a website that could tell me?

I have used weed block fabric and fiberglass screen. The weed block is softer so can be fussier to work with but I like it better. The screen just lets the dirt sift into the drainage later. Your springs and cleaners don't really need access to the drainage layer.

http://www.neherpetoculture.com/vivcaremenu

Once before I had a living vivarium for my geckos! Instead of mesh we ended up using a window screen to separate the substrate and the hydro balls. It worked really well! I hope your crestie loves his new cage.