Parrot MKi9200, buttons can bet attached to the steering wheel or any flat surface within reach using the mounts supplied.
It also has the facility to answer using voice command.
You will need a 'sound on top' harness adaptor, easily found, for about £20. The piggy-backs the Nissan and Parrot wiring making removal easy when the car goes.
Trouble is, partner wants the sort where this is no earpiece etc. Just her smartphone on the dash, set to speaker, so she can press the ‘take call’ button on the wheel and talk at the phone. The cheap system seems to involve wires...