what will be appropriate size of bed for that size of room

the design looks great . According to me one side of windows can be used as bed wall . we can have blackout curtains or blackout window blinds . You can even play with drapery to define the area behind bed. We already have seating in the room so next we can do is give a console/ study table with an puffe / chair to it. also one can add a bench at the end of bed. Size you can check on your Autocad . Bed wall should be the focus when one enters the room, so I feel the bed should be placed like this . Dimensions of furniture and circulation space you can work on. Also WC should be on the washbasin side to avoid Future leakages and dampness in bedroom wall. all the best

There is no pic?!

I agree that your small room can look beautiful. Your floor looks clean, and it is obvious that you wash laundry. Wash your shelves and dry them with a cloth. If your clothing will not get mildew, fold it neatly or roll it (fewer wrinkles) to store it on your shelves. Stack your books and papers neatly - either flat or vertically, depending on the moisture/humidity level of the air in your climate. I see that the wooden bed and another piece of brown wood furniture might benefit from some cleaning followed by an application of furniture wax. I see that the pink base for the desk/table by the bed would benefit from wiping with a damp cloth. Wipe off all surfaces of your chairs. I see that the wall near floor level is discolored. Find out what might be done to clean this. You can make this room clean and beautiful! Best wishes for success.