For me, we need to look at these positions, assuming the players that are already in the XI are in top form:
Courtois
Azpi - Zouma - (a) - (b)
Matic - Fabregas - (c)
Willian - Costa - Hazard
At (a), I'm looking for a classy ball playing centre back, so someone like Stones would be a good fit. If we bring in Christensen in the future as well who's having some great development at Gladbach then we'd have some excellent young centre backs for the future, with someone like Cahill backing them up.
At (b), I really want to see Kenedy have a go there, I believe he has massive potential there if he learns the position well. We also gave Ake out on loan so when he's back, those two can fight for the LB spot.
At (c), we have the option to let someone like RLC develop or get in a proper CM. Ramires isn't good enough IMO so I would like to see an improvement on him there.
We also need to improve our quality in depth.
From now till the end of the season, my starting XI would actually be:
Courtois
Azpi - Zouma - JT - Kenedy
RLC - Cesc - Matic
Willian - Costa - Hazard