For witcher 3 a GTX 750Ti would do just fine and that's what I recommend if you are in budget. Or maybe going to the GTX 950 one of the most budget friendly cards out there and performs close to the GTX 960. from AMD side, I would recommend the R9 270/X or the R7 370 if you have more budget. All of these cards would perform just a little bit below the GTX 960. I play Witcher 3 With my GTX 960 2GB with settings of ultra, Foliage set to low and a little bit of high, Hairworks on and will provide you with a decent 36+ FPS in cities and 52+ in the forest or open space on a 1080p Monitor. i7-3632QM, you're using a laptop so no way to fit these graphic cards in there. Anyway someone else could find this helpful or maybe if you have a desktop.
GTX 750Ti Price: $149
R9 270 Price: $170+
R7 370 Price: $180
GTX 950 Price: $160
GTX 960 Price: $190+