One of the first things that surprised me when I arrived to Japan was how much of the daily life inside houses happens laying down on the floor. Once you get used to it is nice because you can sit down wherever you want. The fact of not depending on chairs gives you a certain feeling of freedom.
But it can also be uncomfortable if you want to be a long time sitting down in the same position. In this case the best option is to use a zabuton 座布団, or much better: a zaisu 座椅子.
These are pictures of one of the most popular zaisu right now in Japan. It is used by gamers because it has an arm rest designed to hold the weight of your arms when you have your hands facing the screen with the game controller.
You can buy this chair here.
