With the room being so small it seems like it it might be impractical to install a shower cubicle with the end result seeming cramped
Have you considered making a 'wet room' instead, so the entire room that you make becomes your shower cubicle effectively. This would make a more interesting addition and probably add more value to the house
http://www.toppstiles.co.uk/how-to/create_a_wet_room.asp
I think it's too small for a wet room!? ie: Water would reach all the way to the door (1 meter or so away) and there would be no way to dry your feet off on a mat for example before exiting into the bedroom.
I do think it makes more sence to have that 80x90cm square space (with a small mat, sink, mirror and towel rail) which really is nothing more than a walk thru into the neighbouring shower.