Sue Says
Coxs Orange Pippin is reputed to be one of the most flavoursome apples so it is not surprising that your family prefer them to other varieties. However, they are also reputed to be one of the trickiest to grow well! They are particularly affected by climate and prefer a mild, dry fruiting season. They are also rather susceptible to disease and need a careful pruning regime to get the best crops. However there are many offspring of Cox that have tried to overcome these problems, particularly improving on disease resistance. Fiesta, Ellisons Orange and Pinova are but a few.
Although you mentioned that you were looking at a self fertile tree, I would always recommend growing it close to a second apple tree with the same pollination group (similar flowering period) if you have the room. This will improve pollination and increase your crop. Of course, if you have plenty of space then you could always try our Britains Favourites Collection which includes Coxs Orange Pippin.