Thank you for your answers!

Allergy sufferers should use an air purifier that is powerful enough to drag all of the air in the room through the filter a minimum of 4 times an hour (ACH) for it to be genuinely effective. To get around 4 air changes per hour in your room measuring between 31 and 40 m² you need an air purifier with a clean air delivery rate (CADR) in the range of 300-399 m³/h. CADR rating indicates how fast an air purifier can clean the air within a particular size room. It provides a way to compare air purifiers taking into account both airflow and a filter's efficiency.

An air purifier with a HEPA type (H10-12) filter is sufficient for most allergy sufferers as it captures up to 95% of airborne particles greater than 0.3 microns.

Most common allergens like pollen, mould spores, pet dander and dust mite faeces range from about 100 microns down to around 0.3 microns and so are easily filtered out by a HEPA type air purifier.

For a bedroom or baby room, you may want to use a quieter air purifier that comes with "night" mode. Air purifiers with "night" mode run quietly in the background allowing you to enjoy clean air while you sleep.