Still are you sure your able too handle the investment of a monitor lizard honestly if you want a big lizard get a tegu they have a calmer disposition compared too a monitor and honestly that habitat is not big enough for a monitor/tegu and may I remind you just got your first reptile which is a crestie which are the polar opposite of monitors/big lizards(caiman lizards, tegus, iguanas, water dragons) if anything get a pink tongued skink which will be perfect for that habitat
unlike their heavy weight cousins the pink tongued skink is an arboreal species of skink and they have have almost exactly the same care as a blue tongued skink.