The tank looks good, but if changing the substrate is necessary (I dont see why this needs to happen), just use newspaper/ paper towel or for a more decorative/ pleasing look, use Astro Turf.
In the future, once Robbie has moved out- you are open to a variety of animals that might live happily in that style of enclosure. Depending on the size, you could think of: Spiny tailed Geckos, Leaf Tailed geckos (Saltuarius sp & Phyllurus sp), Ring Tailed geckos, small arboreal dragons (might need to renovate abit) or small arboreal skink species. Maybe even some Pygopod sp.
Hope this helps.
Shawn