My thoughts about our winter reinforments: the absolute need is another midfielder, someone who can provide some rest for Stefano Sensi.
Some options:
1) make a deal with Salzburg and buy Szoboszlai & Haland duo. Both are teenagers, have a lot of talent, experience from Champions League and should cost about 50 mln euro in total in my opinion. Szoboszlai looks like younger version of SMS with great passing skills, physicality and ball control. Haland on the other hand could be great replacement for Lukaku, because he is doing great in aerial duels. The weakness of this deal is lack of experience of this duo and I guess it will take some time until they adjust to Conte's tactics.
2) immediate reinforcement with someone with experience like Rakitić, Vidal or Matić - I would prefer a loan option, because I can't imagine paying above 30 mln euros for one of them. All of them have nice skills, experence and could be very helpful in the second part of this season, especially Barcelona's duo. Vidal would be great, but if I remember correctly Marotta get rid of him during his Juventus times, so I have doubts if Beppe is seriously considering him as an option.
3) expensive and difficult one with SMS, Tonali, Donny van de Beek - three great players for now and for future. I would love to see Donny here, because of his scoring skills. Moreover, I think he is the most flexible of this trio, because he could play on Barella's position as well as on Sensi's position while Tonali can play only as regista (it's difficult to imagine him playing higher) and SMS can play only on Barella's position. By the way, I would love to see Biraghi, SMS, D'Ambrosio on the pitch and 3-5-2 formation with Biraghi crossing to the box with Lautaro, Lukaku, SMS and DD inside. It would be so dangerous for the opponents. The same way Atalanta is scoring a lot of their goals.
4) cheap option with Rodrigo De Paul - guy who knows the league, knows the language, has nice passing skills, ball control and shot from outside the box. Moreover, can play along with Brozo and Barella in 3-5-2 as well as in 3-4-2-1 with Politano behind Lukaku's back. I bet he can't wait to meet with Candreva on the training field.
Decision depends of our real goal. If we want to challenge Juve right away (so we are taking Rakitić for example), or if we are thinking about next seasons.