If Stones delivered and played at Laporte's level, I don't think we'd buy a CB unless Nico forced a move.
Eric Garcia is probably going to play 5 games before Christmas and maybe 10+ overall and that'll tell us whether he's good enough, but if he is, then Potential-fulfilled-Stones, Laporte, Otamendi, Garcia and Fern would be more than good enough as a group.
It's only if Stones has another season like the last 3 that we'll have to buy, and probably sell Nico and bring in someone to start ahead of Stones.