Geckos would be great for that size! Although I disagree with Pinefamily, if you tip that enclosure so it's longer, it will fit a pair of the smaller species of skink such as L.guichenoti etc etc though some of those can be difficult to track down if you don't know where to ask. I'm not 100% sure on this but as is standing up, a E.striolata might work as well, but I'm unfamiliar with the correct sizing requirements of E.striolata. Btw if you can get one of those large shallow Sistema containers from woolworths or nay grocery shop and put 4 holes in each end on oppiset sides, that will fit a single terrestrial gecko such as N.levis and U.milli quite nicely.