I'm looking for a snake with these characteristics.

[SerpentineDream]

Hmm... Russian rat snake? Another good option is a Trans-Pecos rat snake but those might be harder to find where you are.

Neither is known for being aggressive and both--especially the Russian rat--are active. Both are pretty easy to care for, which is an important consideration. The Russian rat is semi-arboreal and needs a cage that is tall as well as large. Trans-Pecos rats are more terrestrial. Russian rat tends to be bigger both in length and girth but usually stays under 6 feet. I think the biggest of my Trans-Pecos is 5 feet.

I would say the Russian has more of the super active, curious personality but the Trans-Pecos has a bit more of the look as far as head : neck ratio. The Russian looks a lot like a mangrove snake Boiga dendrophilia but without the nasty bite or volatile temperament and the head isn't as differentiated. The Trans-Pecos is actually cute, with bug eyes and very soft skin. The Cape house snake *looks* like it should be dangerous, with elliptical pupils and the long spade head shape, but it's really not.

Another consideration is a Cape house snake. They are slender and small--males around 2 feet, females 3 to 4 feet--but have loads of personality and the Cape subspecies has the look you like. They are semi-arboreal and like to climb. House snakes are rear-fanged but the bite doesn't cause any reaction in most people. I am unusually sensitive to it and the worst that happens is my hand gets puffy. Get them young and captive bred and you probably won't have much of a problem with that anyway.

ETA: The Australian genus Antaresia has some snakes you might like too. They have the slender wedge-head look and stay small like house snakes. I really enjoy my Stimson's pythons. Others are the spotted python, children's python and anthill python.