Do you want a complicated or easy solution to your problem? Here are your two options:
1. This is the complicated one. Follow the American English model:
Use 'holiday' for certain special days, or special times of year, which you celebrate for religious or cultural reasons, for example, Christmas, Easter, New Year, Liberation Day on 25 April.
Use 'vacation' for longer periods of leisure when you have time off from work or school. This can include 'going on vacation', when you travel somewhere for pleasure or relaxation.
2. This is the easy one. Follow the British English model:
Just use 'holiday' for all situations. Forget about 'vacation'. It isn't used in British English.