We need a superstar - a Bale, Ronaldo, Salah, Hazard, Aguero type.
Forget 4 players and just wet the bed and go full muppet mode for that 1 player.
We got our star player 2 summers back in Pogba, and he's still got questions-marks placed above his head as to whether he'll be worth that fee.
I personally need to see some wide-players who can bring some directness into our play instead of the constant habit our players have of moving inside the field. It would be a brilliant tactic IF we had proper fullbacks who won't constantly take too many touches and slow down our play, but if Young and Valencia are going to occupie those positions next season, we simply need players, who are actually capable of dribbling past his opponent. Sanchez, Lingard, Rashford, Martial and Mata can't do that and that for me puts the responsibility of our attacking play onto the midfield players to provide cutting passes and since that won't happen either, that'll provide us with this dire form of football, which we've been served for the last year now.
My 4 signings would probably then be Savic, Sandro, Alderweireld and Willian (for the quick-fix on the right wing), but we're still suffering from Valencias lack of attacking capabilities.
De Gea
Valencia - Baily - Alderweireld - Sandro
Matic
Pogba - Savic
Willian - Lukaku - Sanchez