Don't buy them. You will spend millions buying bluerays then in 6 years they will be replaced with red tail super high definition 3D mega discs, meaning your bluerays will have to be stored away with your DVD and VHS collection.
Instead simply subscribe to sky movies and Netflix and enjoy yourself
My DVDs all work quite well on my Blu-Ray player. I bought some of my favourites again in HD but am happy for the rest to stay in SD.
DVD is far superior to any streaming service I can get and better value for money than Sky Movies.