If we continue to play Mata on the right, who will naturally come inside, then having someone like Griezmann would be perfect, in my opinion.
He would provide loads of running off the ball, which will allow the likes of Mata to tuck into the middle and have the room needed to create.
A front four of say:
Lukaku
Martial Griezmann Mata
Would be very similar to France's front four, in that you have a winger who is looking to run at players (Martial/Coman) a target man (Lukaku/Giroud) and someone who comes inside from the wing (Mata/Lemar). Then you obviously have Griezmann behind the forward.
92 million, in this day and age would be money well spent, in my opinion. He's a goal machine, and would take pressure off Lukaku.