Myrtle Ave, or somewhere close by, would be OK for the 09R departures. (My wife and I prefer the entrance to Feltham Cemetary when 27L is the landing drag - very good for pics from there).
For 09L, it's difficult. Plenty of people park on the "pavement" on the A3044 just south of where the 09L approach crosses but it is dangerous as it's a very fast road. Photography from there is excellent but you might be moved on. Maybe a small side road in Poyle would be a good place??
On-airport viewing is almost impossible nowadays..
Good luck..