No, you don’t need to double the tuition fee to account for the extras.
The biggest ones are likely to be coaches (you might not be using them) and lunches (some schools, packed lunch is an option) music lessons (if applicable) and foreign trips (optional) and uniform (many will buy from the second hand shop). You also pay for public exams which is about £500 for GCSEs. Other things are cost if day trips, lost uniform, some clubs which might be extras.
Definitley run the numbers for fee increases of 5%, 7% and 10% and remmeber to compound the increases over the 7 years. The fees may well have close to doubled by the time you child leaves.
So, yes it would be useful to know the fee increase before deciding, but to be honest, some schools will increase by more than another some years and then that will be the other way round the following year….so this year’s fee increases alone don’t tell you who will have the biggest rate of increase over 7 years. You can only look at the starting point of fees now and assume there will be at least 5% rises each year.
If it’s a struggle at the start, unless you’re going to come into money or have definite large salary increases looming, it’s probably unaffordable.