Probably need both.
Would it cost a lot? Sure. But it's the club's fault for not signing properly the last few years as well as letting a player like Thiago leave. So now we have to pay for it, literally.
We can argue about cost and alternatives, but the truth is that we need quality right now. Both would still contribute for 3-4 years which allows you room to develop other players from the academy or scout for younger talent, as well as using Messi's last years at the top level.
We need more creativity from the midfield and someone who can score goals up front. Coutinho and Griezmann are the most available options. I think Liverpool will let him leave for a not so crazy price in the summer just like they did with Suarez. They already have his replacement in Naby Keita. Not the biggest fan of Griezmann, but the reason he's struggling at Atletico is because he's heavily isolated with them having no resemblance of any attacking play or tactics.
As for that controlling midfielder then keep looking. Unfortunately not an easy position to find a quality player in.