With all due respect, the jump from a pet as easy to take care of as a ball python to a monitor is no comparison. Yes, adult Iguana's can be a handful from what I've heard but still a long way off; how long have you had yours?.
I suggest you do a ton a research, both here and on the many other monitor specific forums available. In the long run, it will help you make the most informed choice for yourself and the future of the monitor you choose. If you are questioning the ability to give it the enclosure it needs then perhaps a smaller monitor, although not what you think you want, is more in line with what you can actually accommodate. Monitors don't lay around like snakes & Iguanas, when they are active, they need their space.
I went from breeding Red tailed boas and Burmese pythons to my monitor and there's just no comparison. I don't consider myself an expert by any means but I did do a lot of research and suggest you do the same, the results will be very rewarding.