If we want to go like for like - I agree Ojo is probably our best option.
I have suggested playing a diamond, as it for me is the formation that suits Sturridge the best. However, I'm not sure at home it is the best approach to go, as everything could get a little narrow. The diamond also didn't work terribly well the other week when used vs Man U, however I think that was more the players playing poorly that day than the formation being at fault.
Whatever formation we choose, I think Lallana has to be deeper. He was a key part in us doing well at the beginning of the season and him looking like a different player to the one we had previously seen at the club, by playing in midfield. He can be a play maker in that role and Wijnaldum and Can, for all their strengths without the ball can't offer what Lallana (or Coutinho when he's used in midfield) can. I believe it makes a big difference.
What I don't like is seeing us play one of Lallana, Sturridge, Origi or Firmino wide in the front three. None of these players suit that role, for different reasons.
If we were going to buy, then surely we do it it earlier as Mane has already missed a few games. So that's not really an option anymore IMO.