It's not that complicated!
The first thing you need to establish is when your Bus was built from the chassis number. Was it built before August 1st 1970 or after?
If it was built after August 1st 1970 then the one you have highlighted will suit.
If built before, Heritage would appear to do one (211 611 021 T) for £73 prior to any discounts etc.
The above assumes that you don't have a servo.