Vlahovic. Stock is low and with Juve's troubles he's probably attainable. If he rediscovers his form from around mid 2020 to mid 2022 we will have a proper striker on our hands.
It would also give us enough depth to compete on all fronts with a front six that looks like this:
-----Martinelli----------Vlahovic---------Saka-------
---Trossard/Jesus---Jesus/Trossard---Jesus/Nelson
Enough games to go around for everyone (except maybe Nelson) and depth to change things up when it gets stale.
In addition, we would still need the following:
- RB/CB (Simikan?)
- DM (understudy for Partey)
- Xhaka replacement (Rice)
That's what I'd be aiming for this summer.