A few of months ago, I had Braybrooks expertly install a Pioneer sph-da77dab for £850, and it has been working well ever since.
With options for Standard, Bose, and Harmon Kardon audio, as well as different versions of the command, NTG, and ancillaries (CD changer, phone, satnav, etc.) installed, it may get difficult as to what has to be added, uninstalled, or bypassed. So, you'll need to do a significant amount of study.
You can find all the necessary components at InCar Tec or a similar store if you're handy; however, any 6.8-inch double-din head unit would serve as a suitable substitute for the pioneer (at least in my opinion; I must admit, I'm not that knowledgeable about vehicle audio, which is why I opted for Braybrooks).
In addition to being more accessible than Braybrooks, the command staff online are well regarded. It would be wise to enquire about their capabilities in installing aftermarket head units.