Ideally we need someone who can come off the bench and make an impact, and doesn't take 6 or 7 games to get into the swing of things, given then anyone we buy will be backup to Aguero. But we also need to accept that players that are willing to come and play that role aren't likely to be world class. Bony's a top class striker, and probably as good as you're likely to get in that role.
Look at other teams and see who they've got after their main striker.
Chelsea: Remy/Falcao
Rags: Wilson (or put Martial or Depay in the middle)
Arsenal: Walcott/Giroud rotation, Welbeck
Bayern: Kids (or put Muller up front)
Barcelona: Kids (or move Messi/Neymar into the middle)
Real Madrid: Jese (or move Ronaldo/Bale/Rodriguez up front)
Most of the really top teams don't have a decent backup striker, they rely on world class players that are able to play a number of positions if someone is injured. Hopefully we'll be able to do that in the future with Sterling and De Bruyne being comfortable up front scoring goals. But as far as dedicated backup strikers go, I'd say Bony is as good as any in the world.