If Griezmann doesn't come I'd sign two MFs.
Eriksen and Thiago would be perfect for me at this point. Both approaching their prime years, experienced and proven on club and international level, and would inject world class level into our midfield immediately, so young players like Arthur and Alena wouldn't have too much pressure on them right from the start and could learn from them and have enough time to really settle into our club and prove their worth.
As for Eriksen and Thiago, we could get them both for 200M, even 170-180M if we do some successful negotiating. And this way we would sort out our midfield and finally give Messi and also Suarez a world class midfield behind them again and hope they get better (Suarez) and can focus on attacking rather than play making all the time (Messi), and give all our senior players remaining at the club realistic chances for a few more UCL trophies before they leave/retire, mainly thinking Messi, Busquets, Pique, Suarez and Alba right now i guess.
Two world class midfielders were always my preferred choice...we can always push Coutinho up front and bench Suarez if he's not in form, so his starting spot would still be more endangered than it is now. Not to mention new great attackers are breaking out almost every season now, we will have so many great options in the next few years in players like Mbappe, Werner, Sane, maybe even Kluivert Jr, if he properly develops in the next 2-3 years. Heck, there's even Dybala after Messi leaves as a direct replacement (i think there's no one better than Paulo for that role, but only after Messi is gone). We can look for direct #9 or wingers, depending on what's gonna happen with Coutinho, if he would keep playing LW or move back to midfield in time. In someone like Werner we could actually get both in one player, not that i'm saying we need to get him exactly, even though if we would want him, we'd need to go for him, as long he's in a mid-level club like Leipzig and before he ends up at Bayern, which he will sooner than later as the Lewandowski's successor. There's even been talk about it this summer already, ever since it was reported that Lewa was becoming unsettled and wanted a new challenge. We should be looking at players like this, not after they first go to another big club and become world class there after 2-3 extra years, and their price immediately jumps to 100M+. Fabinho comes to my mind at this point too, just went to Liverpool for 50M, where he'll probably start bossing it right away and be worth twice as much after 2 years. We need some serious scouting improvement for that though. And a new, actually visionary Board would be nice while we're at it, but that's a problem for another day (or should i say 3 years until 2021 at least).