As above you have a few option.
Keep the Bose and get a Nurrish satnav, not used one but they look very good.
Get an aftermarket HU with satnav all singing and dancing. This is what I have and lots of others on here too, everything works i.e. steering controls and as it has it's own Bluetooth no worries there either.
All depends what you want and how much you want to spend really, Nurrish nav I believe is £400ish and you could always replace the Bose separately too... A Pioneer like the one I have is around £700 and improves everything including sound quality, complete ipod control, parrot BT and still have a cubby for any other bits, I have had a speed controller and now maybe a dab radio...