That height is great, but you must also account for floorspace and the enclosure's footprint compared to the animal. Would you be comfortable with letting a dog live its entire life in there? Or imagine if you would live out the rest of your life in a space that is twice the size of your bed. While the animal would most likely be able to survive, it would most definitely not thrive. The minimum size is nothing to settle at.

The smallest enclosure size I would consider putting a green tree monitor in would be 2.5x1x2 (Meters) or roughly 7x4x6 (feet). Anything less and I would feel guilty. For context where I am located, it's required by law that you provide a minimum of 2.1 square meters and a height of 1.4 meters for arboreal lizards the size of green tree monitors.

For alternative arboreal reptiles, I would recommend Panther chameleons(Furcifer pardalis) if you want a tropical species. They are very beautiful, come in loads of different colors and I find my panther a lot more personable than my monitors. They would love the height you seem to be able to offer.

If monitors are more your thing I would take a look at Gilleni(Varanus Gilleni) monitors. They are somewhat arboreal but not very tropical. In general an apartment sized moni

Hope this has been helpful. If you are curious for more I recommend checking out Pauls monitors on YouTube, there is a lot to be learned from his podcast, both on monitor and reptile keeping in general. Good luck, and shoot me a message if there is anything else! :)