This is the link to the RHS site on apples. hope it helps.

I would lightly tip prune in the winter to make it bushier. It seems that the harder you prune the more vigorous the tree will become. Your greatest problem will be the need to either transfer to a very large container but best to replant in the ground. In a container the roots will eventually displace the soil and if you forget to water regularly your tree could fail.

If it was sold as a patio apple it will not get too tall in any case. What variety is it?