Absolutely Mad: With all those suggestions youre probably a bit confused by now but let me assure you an eastern blue tonged skink will make an ideal starting point.
As your enclosure is a little small at the moment, why not consider a baby bluey. There will be a lot available in the next few months.
As much as I love the dragons, in my opinion, a bluey would be a great introduction to keeping reptiles.
Good luck and whatever to decide, ENJOY the experience.