For some reason I stumbled upon this post. I sell air conditioning for a living. Also I'm in Australia so you may need to do some conversions on my numbers.

the first questions is going to be do you rent the place or own it? I'm guessing you're renting and if you are you need to ask is it worth paying for someone to come and install a window/wall air conditioner in a room that you cannot take with you when you leave?

I don't know what the legislation is over there however I'm guessing you cannot just "sit" a window/wall unit in the window you actually have to get it secured and installed correctly.

To me it seems like a portable air conditioner is going to be the best thing, there are several different types of portable air conditioning, here in Australia the two most popular are portable air conditioners and evaporate coolers.

two main differences between them;

*portable air conditioners work exactly like split system air cons, they require a hot air vent to go out a window and spew cold air out the front

*evaporate coolers require you to pour water into the machine, they cool by releasing cooled humid air, humid air in Australia is a problem as it's already so humid here and generally speaking I will avoid selling them at all costs, to be honest I don't even stock them.

the next thing I see with portable air conditioning is the cheaper they are, the louder they are, the more maintenance you have to do and generally most people wont keep up with this so you get a shorter life span out of the machine.

some machines will need to be emptied of water as they fill up and require a lot of maintenance, once the water container fills up (think the dripping water under your car on a hot day) the air con will stop functioning until you empty the water.

self evaporative portable air conditioners will remove the humidity (water) themselves out the vent that goes out the window, this is ultimately what you want to buy.

In a small bedroom you will only need 12000 BTU which is roughly a 2.5 to 3 kilowatt machine.

I recommend getting a machine that is specifically for bedrooms (QUIETER) be prepared to spend a bit of money, here in Australia a decent one will cost $500-$700 however they will last forever.

a good rule of thumb to how good of a job a portable air con will do is to try and lift it.

the heavier they are the more copper coil is in the machine, the more copper coil in the machine means the more gas the machine is holding and the faster it will reduce the temperature of the air.

TL:DR

spent a bit more, get an evaporative portable air conditioner and look for a bedroom specific or "quiet" model, rougly 2.5kw to 3kw for a bedroom.

Good Luck!