Regarding possible names, Bacca is somebody to keep in mind. He is extremely frustrating, but when on form, I think he was even ahead of Jackson Martinez in pecking order for their national team. May be still is.
A bit like Bony, but may be pacier and more mobile. Not the very top bracket, but a very decent option nonetheless.
Vietto seems a talent playing for Villarreal, though not proven at all. I also think a good club should have gambled on Leo Baptistao by now, don't know about work permit possibility for these guys though.
With regards to Origi, expectation is high, may be too high? If he comes in January, he will find himself under an immense pressure to score, and looking at his scoring record, his output is not much different to Balotelli's, i.e. 1 in 5 or 6.