This is what we recommend based on your details:

Ceiling Height.png

2.4 - 2.6 m

Room:AreaSize.png

4 x 4

Based on a ceiling height between 2.4 - 2.6 m, and an area size of 4 x 4, we recommend a 12,000BTU unit. 

Some options:

Available in 12,000 BTU

Toshiba High-Wall Inverter