Hi Bob and welcome to the forum, I went to monster car audio and spoke with them to find one I liked that not only did all I wanted as far as Sat Nav but had all the bells and whistles as far as audio, phone, video for rev camera etc, they installed for me as it requires the right harness to have all the steering wheel buttons work, Plus the surround to fill the space that the old head unit leaves when removed.. I would not tackle this myself as I did not want anything to short out because of something i did..I would suggest if you are planning on doing this yourself to at least talk to a good audio shop and see what they can offer as far as advise..There are some excellent head units out there so a lot to look at and with Christmas and New Years sales very close some great deals as well
Let us know what happens mate and Good Luck hope it is sorted quickly for you
KAA