Great transfer window so far. Getting 150m for non-starters is truly impressive. As much as I appreciate Ake and Sterling, I don't think they are vital for us in the big games. The only one I think is very important for us is Jesus. His pressing and link-up play in the big games has always been superb.
Anyway, Chelsea is not our rival for the title, so making them stronger is not that big of a deal. Also, they have lost Rudiger and Christensen, and both are better than Ake (or at least Rudiger for sure is).
To replace Ake, I would play it risky. After all we are talking about a 4th CB. Someone young and inexperienced (outside of PL), but with a lot of potential. Maybe Serie A or Ligue 1 defender.