Liverpool already have players who can play in the number 9 position in firmino’s absence. Darwin Nunez and Cody Gakpo are both capable of playing in that position while Dias and Jota play on the left flank, there is no problem of getting a replacement for Firmino except Jurgen Klopp decides he needs an extra pair of legs to boost the depth of the squad but outside that I think Liverpool need to bring one or two defenders in this summer and they are good to go.
Liverpool can just add an additional player in attack that can be a backup for Gakpo.
What I think they really need now is a central defender. They are going after Levi Colwill but that will not come cheap. I don't believe he's worth the price but I also believe Liverpool should go for him. He is a very decent center back and he will make a very good pairing with whoever Klopp decides to pair him with at the back.
I also feel Liverpool needs another central midfielder to add to MacAllister and Szoboszlai. These two players and very good players that would defiantly strengthen Liverpool but I feel a third should be added. A player with equal quality so they have quality squad depth.