One easy way to make your space feel comfy and look amazing is a curtain. Personally, one of my favorites is the Sunflower - Lavender - Curtain.
This curtain measures 44" x 88" so if you have a small window you will only need one, but if it's a medium or large window you might consider getting two or three.
There are a couple things to consider when measuring for new curtains. You want to make sure that you start measuring a few inches above the window. It'll make your ceiling look longer and the room will feel bigger.
For this curtain to work you will need a curtain rod. But you can buy them for cheap at many local stores.
So, the curtain was a little thin for my taste. When I want the sun out, I want it out! But if you enjoy the natural sunlight then this might be the curtain for you. You can always add a curtain liner if you find it too thin also.
What I like about this curtain is the design on the cotton fabric, though over time it does fade a little, but you can always re-purpose it and make something new!
Another great way to use this curtain is to use the same rod you have for the window, but instead place it behind your bed and decorate with Christmas lights for an inexpensive headboard.