Hi, I don't grow veg or fruit trees, but if I'm not mistaken, a 'Braeburn' will be suitable as a cross pollinator, it doesn't have to be a Cox's orange pippin, as long as both the trees flower at the same time, Derek.

Cox's Orange Pippin is flowering group 3. So, any other apple with group 3 will be best. Having said group 2 and 4 will also be ok. Google apple flowering groups will give the info. A Malus (crab apple) will also do the trick as they tend to flower for some time. If possible, I would consider replanting your tree in the ground during the winter if you have the space.