The problem with windows usually lies with small, glass enclosures. It leaves the critter without anywhere to go and you run the risk of heat stroke. That typically isn't a problem with large, wooden enclosures, but I would still keep it closed just to be safe.
As for species, I'm going to spitball various species of different sizes, lifestyles, and handability, just to get a better idea of what you are looking for in the animal itself.
A Columbian Redtail Boa could easily fit in that space, and while they do benefit from a bit of height, floor space is more important. Most tame down to be little puppy dogs by adulthood, although you do have to be prepared to deal with a ten foot, aggressive animal as you would any species.
Slightly smaller is the carpet python. There are several subspecies that varies in size and coloration, and while the coastal females can get up to the length of a red tail, they still don't have the thick bulk of muscle that they have. There is debate about how much height they need, but rest assured they do need it (these buggers love to climb). They tend to be snappy as babies and mellow out some as they mature, but they don't get to be as tame as some red tails and a good chunk remain aggressive without the socialization needed at a young age. The three most common subspecies are:
Irian Jaya Carpet Python (5 feet in length)
Jungle Carpet Python (5-7 feet in length)
And the Coastal Carpet Python (9 feet in length)
The biggest snake I would recommend for you is a Burmese Python, and that's because of how docile they are and they're some of the easier of the giants to care for. Typically they are around 10-11 feet in length and while I've never had one myself, there are people on this board who has and most are pretty laid back and tame. Still, you have to be prepared to deal with an aggressive individual which isn't very wise without at least one more person to help.
The last snake I'm going to offer is a colubrid. I'm going to mesh the racers and beauty snakes into one suggestion here since they seem to be pretty similar except for care requirements. These are diurnal, robust snakes that are great display animals. In the wild they are always moving, always traveling, and they can travel some great lengths in search of prey, shelter, and mates. They're both pretty great and I plan on getting one actually. I wouldn't count on either to be tame though, as they both tend to be aggressive and quick (especially if they are wild caught or just were never handled). The black racer is only 3-5 feet in length, but they still relish the large enclosure that a boa would need since they're just always moving. The Taiwanese Beauty is 6-8 feet in length and still needs a good size enclosure, preferably as long as the snake is. Neither really needs a lot of height, although a couple feet and some branches never hurts. If you can find them, another I can suggest is the Ridley's Cave Racer (up to 7 feet in length).
Black Racer
Ridley's Cave Racer
Taiwanese Beauty
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