Just buy an absolute top level.. or dont buy at all (,and just keep playing Cancelo/Zinch there). it will just be another Angelino scenario then.
So my suggestion would be Guerreiro, if not his injury issues keeps popping up.. (feels like he has had a lot of muscle issues the last couple of years) Hes one of the few that is world class in multiple roles as a left back as well. Inverted, wide, could play tucked in in a 3 back in the build up as well. Theo Hernandez is a more of a wing player only and not as flexible.
And Cuc is not there yet, and has few pure top level attributes. The others on the list might develop into it, but it not there yet and will be similar to the Angelino-scenario that I brought up earlier.
And I feel, as an avid La Liga watcher, Gaya is too small for the Prem really.. and not physical enough with pace, power etc to make up for it either. He doesn't really have that great of a left foot either, great character similarly to Cuc though.
I would love Porro "back" for rightback-rotation and just play Cancelo left..
Theres a lot of (other) priorities in this team, maybe with Gundos alleged ongoing issues as well etc.