Have you considered having your existing radio upgraded? I've come across this company who offer that service I don't know anything about them other than having found the website and I have no connection with them.
https://www.radiorescue.co.uk/fm-and-dab-upgrades/
I'm thinking about using them to update the radio in my AC. The best option I've seen would be a Becker Mexico (retro) which has navigation as well as everything else but even if you could get it second hand it would still be in excess of £2000.