Sprint Navigation Mounting Sprint St (2000)

Hi there,
I'm new to this forum, I have bought a 955i Sprint ST, 2000 model(pic attached), it is an amazing bike in magnificane condition, love riding it every chance I get.
I am looking for the best (and easiest) way to mount a cell phone (iPhone7 Plus) to use navigation app etc.
I have looked through several options, the only one that looks correct to me is to mount it by replacing the central nut on the handlebars with a ball joint contraption. I would like to know if anyone has already done this successfully and then give me some tips and pointers what to buy and how to fit etc. As it is the steering, I don't want to buy the wrong thing.
Thanks for any advice.
Dinsdale

 

Thanks Crispey for the really quick reply, I have checked them out already and the solution to my question is ready to go.
Thanks again
Dinsdale