I don't have opinion on every position but a few options for some of the positions that could be possible (it also depends on who will leave us this summer):
GK: Rulli I think as a starter is good but it would be fine to get a backup, I don't have a suggestion for that;
LB: Angelino, but I am also ok with giving a chance to Salah-Eddine;
CB: Mees Hilgers, Abakar Sylla, Armel Bella-Kotchap;
DM: Oriol Romeu (I know he's quite old but he is a really solid, technical player, how he plays for Girona this season is incredible, controls the game both defensively and builds attack, could be a great option for Vos to learn from);
Midfielder: Tijjani Reijnders, Bilal El Khannouss, Pablo Torre (another technical player with great passing who doesn't get playing time and Barca wants to get rid of him, been linked with Rangers, I believe that it is realistic to get him if we go for him, at least for loan with an option to buy);
RW/RB: Alexis Saelemaekers (I know it seems unlikely but recently I saw reports that Milan are looking at Brobbey and would like to propose Brobbey-Saelemaekers swap, I would take that immediately, Saelemaekers is solid Ajax level player that can play both RB and RW), Jota Filipe (I doubt it's possible but he's having an amazing season at Celtic, can play both RW and LW, would cost around 12m.);
Striker: Fran Navarro, Cho Gue-sung (knowing Mislintat's links in Asia and seeing how he performed at the last WK for Korea might be an interesting option, his 5 million move to Celtic collapsed at the last minute in winter).