Travelling with infant abroad without the father

I am the mother a 2 month-old, and planning to travel abroad in May without the father. I am an EU citizen, married to the father who is a dual citizen, EU and British. Baby has a British passport. We will be out of the Uk for over 28days and the father is aware and condenting to this trip. Gov.uk mentions that I need to have a letter from the father with permission from him to travel abroad. I understand it's better to have this than not, as I might get asked for it. Does this letter need to be notarised? Do I need to speak to a solicitor?