You could use a 3x2x1.5 tank for an IJ or Darwin as long as there is at least one perch.
Yafe, my IJ/Darwin albino hybrid, is in a 4x2x1.5 with two perches. They really do need at least 1.5 of height though. If you give them that, a perch or perches, and hides, they will spend much of their time out. However they are nocturnal.
If you can go longer like a 4 or 5x2 tank or bigger, a bearded dragon would be cool and if you can go 5-6x2 Blue Tongue Skinks are great too. They are also easier to feed/lower maintenance than a beardie.