Taylor Harwood-Bellis could be ready within 18 months - he’s simply that special. With him in mind, we shouldn’t be be spending huge money on anyone young like Dias or Soyuncu; I’d get Alderweireld, who’s an upgrade on Stones and Otamendi, and will be available cheap in January given the fact his contract expires in the summer.
Skriniar might be viable, as he’s seemingly struggling to adjust to Conte’s 3 man central defence; they might want to recycle him into system-compatible player(s)....but again he’s young and would be a long-term obstacle for THB and Garcia.
Another defender we should sign is Nathan Ferguson; West Brom kid who’s now developing in the fullback positions having spent most of his youth career as a very highly rated central defender. Spurs, Juventus and Atletico are apparently drafting bids. Walker will need replacing soon, so it’d make sense to sign him in January and loan him out for 18 months, rather than waiting for someone else to buy and develop him, then end up paying £50m further down the line.