Hi LYD, if you need a pleasant spot to watch the arriving aircraft, then may I suggest the rear car park of the Premier Inn on Bath Road, there's a nice slightly elevated covered area with benches, there's a Costa coffee, toilets, everything you need. You just can't see the runway though.
Just make sure that the runway direction for approaching traffic this week is actually 27R!
The runway alternation PDF is located here:
Heathrow Noise: Runway alternation