Attics are more and more common these days and furnishing them requires good taste and experience. 

Furnishing an attic is as enjoyable as it is difficult: maybe the slope of the ceiling creates warmth, but it also removes the volume which is useful for the furniture.
An alternative is to level out irregularities with plasterboard; in this way, you can create flat surfaces on the ceiling and use spotlights for illumination.

The second piece of advice we give you is to use sliding doors to recover as much space as possible.

In the day area, choose low furniture such as chests or bookshelves which are placed on the floor.

If, in the bathroom, you don't have enough height for a shower, opt for a bath.  It will guarantee you moments of pure relaxation.

When you have finished furnishing your attic with everything indispensable, you can dedicate yourself to accessories and give your home the character it deserves.