Dual graphics wasn't a good idea, last time I checked. Although your average framerates will be higher, there's a huge amount of frametime variance (the frames don't line up very well) and it results in very choppy gameplay. You're better off just getting a discrete card and not using your APU's integrated graphics.
R7 250 / 250x are good, inexpensive choices.
R7 250 is twice as fast as your integrated graphics.
R7 250x is around 4x faster.
R7 260 is about 6x faster.