I would be happy with two midfielders, Lavia and Caicedo.
Lavia, not ready for a regular first team starter in the 6 role, but there is still some life in Fabinho, and he can be the understudy, seeing action and bringing him through.
Caicedo as our main midfield signing, to be a fixture in the side. I would play him as an 8, on the right side to replace Henderson, who in turn reverts to the Milner role. Comes in, closes games out, starts occasionally, keeps standards up around the club, but not a main player any more.
Caicedo adds much needed athleticism. He is strong in the tackle too. He is also fast and covers a lot of ground. This will be important as Trent develops his playmaker role as an inverted right back. He has been so productive in that role in our winning run, and if we are to extrapolate that over a season it will be very special. The downside is a few more gaps opening up, but an athlete like Caicedo shuts the bulk of that down.
So for me, two midfielders. Lavia and Caicedo. (If Fabinho is departing, I would upgrade to Ugarte, who is ready now). But I am operating on the premise that Fabinho stays, there is still some life in the old dog, and Caicedo will be pricey, £80M or so. Hence the need for a young up and coming plus an expensive midfielder.
Add a central defender to Caicedo and Lavia, and we won’t look back.
Edit: obviously we are looking at lots of players, and it could easily be Ugarte and MacAllister, or Gravenberch, or Kone, or Thuram, etc.
But Lavia and Caicedo would be good.