Short summary: Buy Lewandowski, Recall Lukaku and play them together.
If Lewandowski can be persuaded to leave Dortmund and come to Chelsea in January or the summer, he and Lukaku could be a perfect striking combination. You've got everything needed in an upfront pairing, strength, height, speed, passing ability, attacking position. Admittedly, 3 out of the 5 areas are possessed by the little polish genius, but Lukaku will learn in time.
Lewandowski has also shown great vision in making the right passes in times he could have gone for an unlikely shot, so he can be played a little deeper behind Lukaku, who can relieve pressure on our rather timid midfield by being a target man when necessary.
This would be my starting line-up in this scenario:
Azpilicueta Cahill Terry Cole
Luiz ( Luiz and Lampard playing balls from deep for the strikers)
Hazard Lampard Mata ( Mata and Hazard playing as wingers stretching defense)
Lewandowski ( Buzzing around performing the jobs Lukaku's too lumpy to do)
Lukaku ( Scary beast who bullys defenders)
Hopefully the rumour of Lewandowski's agreed deal with United is false, but what can you do. If he can be pryed away from Dortmund the value would definitely make him a fantastic option, iI reckon we could get him for under 20 million as well.