CD player or I-pod conection for a 2005 C-class

Hi all, My dad has a 2005 C320 CDI. It does not have the COMAND unit fitted just the standard radio/CD unit. he wants to somehow incorporate either a CD Auto changer into the original head unit. we also want to maintain the functionality of the steering wheel controls. We have a few question can anyone give us a hint.

What is it that we need to look for when choosing a CD changer?

How easy would it be to fit the changer into the glove box (as with the OEM Mercedes unit)?

Who makes the OEM Mercedes changer? (Sony, alpine etc.)

Does anyone have a recommendations for a supplier/installer in the UK?

The other thing we could consider would be an I-pod integration kit. Much the same questions apply with that idea, so if you can give us the same hints about supply and installation that would be a huge help.

Thanks
James