Let us do our best with what we have and start planning for next season from now.
I would personally try to secure both Werner and Soumaré this month. Look for a CB and see if we can get Willian for free + a promising RB and move Roberto to the midfield.
Werner
Soumaré
Tomás Esteves
+ talk to Willian and look for a CB. Upamecano should be available since his contract is ending in 2021, but I personally prefer Konaté. However, I cannot see RBL selling him when Upamecano is most likely leaving. Koulibaly? Napoli might not qualify, and I can see them selling him for the right price. We have already got three young promising CBs, we do not need someone without experience.
Once the season is finished, tell the old ones (Pique, Busquets, Rakitic, Vidal and Suarez) that they should look for a club.