I my opinion, just my opinion, you can forget about PSG, Barca, Chelsea in this winter window.. I don't think they will ever let their players go now. My option would be to take Porro in and shuffle around the back. I firmly believe Man City need an offensive outlet for the next 5-10 years from the backline as well and I cant at the moment see where that is gonna come from otherwise. Nuno Mendes would be a dream but hes at PSG and Baldé will be dominating in Spain for the next +decade.
We will probably never see Cancelo again.
Sergio Gomes will probably go to Girona on loan in the summer (will have to compete with Miguel then though) or back to Anderlecht and develop some more, I don't see him as a viable long term regular at City.