I'd be looking to fit Insigne in rather than Mertens. I find him far more effective.
I just sold 87 Insigne, as good as he is, I find him decent at LM, but at LW he gets squashed too easily, no strength, decent passing, shooting is ok at best, Costa is only there as a short term trial, I usually use Perisic there, what he lacks in speed he makes up for in composure & shooting, especially with his 5* WF, plan could be 4231 CAM version with Mertens & SOTW Perisic out wide, Dybala in the middle behind Immobile.
Birthday Felipe Anderson & Asamoah look great, too!