We need at least 3 good transfers in the summer, a top GK, a defender and a top central midfielder.
A top GK should be a priority in the summer: Alisson, Leno and Butland are very good options. Oblak would be the dream signing though.
Another centre-back should be signed to provide competition for Matip: Tah, De Ligt, Jemerson, Gimenez. Jemerson and Tah are looking very good, any of them would start in our side.
In midfield, in my opinion the best options for a CDM would be: Jorginho, Rabiot, Weigl, Ndidi. Weigl and Jorginho would fit the bill the best.
Also Dani Ceballos might be a good option to have to challenge Georginio's place in the team.
These 3 positions are key to improve if we want to mount a title challenge in the next season. Also, another striker to provide cover for Firmino would be great, Werner would be a fantastic signing but the transfer fee would be inflated and he should be a starter in any team, i can't see him fit in our system. Good players to provide cover would be: Luan, Dolberg, Moussa Dembele.
Players to be offloaded: Mignolet, Lovren, Klavan, Moreno, Henderson, Lallana, Sturridge, Ings, Grujic, Markovic, Origi, Flanagan, Bogdan.