Ask HN: How to setup working environment without furniture on the floor?

I have been working on the dinner table, but It's not comfortable because my son is loud. I have bedroom which is empty and I could work there. I want to try working on the floor, but I dont know how to setup good working environment without furniture or how to sit correctly. I could buy little furniture like small folding table but I would prefer to use in house stuff. 

I have rented apartment which I want leave pretty soon that's why I don't want to buy desk or any other big furniture (also I dont have car). I can pack myself and my family to 5 suitcases and I would like to keep it that way. 

Has any of you tried working on the floor? Do you know how to sit correctly on the floor without hurting myself?

Thanks for any advice!