ensuite bathroom -how to join in with existing combi system

Hi,

I am building an extension and adding an ensuite bathroom. I currently have a potterton performa 28i feed my rads and the bathroom. The existing bathroom has a shower mixer valve inside a separte shower.
What is the best way to connect into the system so I can feed a 2nd shower in the ensuite. I have been told to use an 's' plan system with a tank - is this right?

Thanks

Yes if you want to use both bathrooms at once, or buy a Brittony IIt for the second bathroom.

If you have two bathrooms or more your always better to store water so a cylinder would be better I like un-vented for two bath but anymore and a vented cylinder may be better