Hi

As someone who has spent the last 20 odd years developing antennas for cars there are a few options - BUT be prepared sometime in the next 3yrs (if the UK govt is to be believed) FM radio will be turned off.
This will happen all over Europe soon.
At that time you will need to upgrade the radio and as the Digital (DAB) system requires a better signal strength for reliable reception you will need a good antenna.
I wrote an article for Miscellany last year about fitting DAB to my 4/4 but using the telescopic antenna which is standard fit.
If you want to e mail me I will send you a copy plus some info on antennas you can buy.
h.bottomley1@btinternet.com

Howard