Options for RB position are a converted 34y old winger and very attacking minded 20y old kid…
Honestly if we are to choose between gutting the most of our transfer budget to get an overpriced CB or stick with Smalling & Lindelof, I prefer we stick with them 2 and spend big on RW, RB and another MF.
I think our needs go like this, ranking them by the odds we currently have a player who can have a very good season (like the kind Herrera, Shaw or Lindelof is having, don't need to be De Gea or Pogba to be a position of strength).
RW - 10% chance we have a player in the squad who can have a really strong year at RW.
We absolutely need one, nobody really has the potential to have a strong year there in the squad except Rashford and he and Lukaku are our 9s, and he's also probably our best option at LW after Martial. Lingard isn't good out wide, Dalot doesn't seem like a strong RB and while Lukaku does well enough out there, that's probably more of a specific tactical counterattacking move than a week to week thing under Ole (I do sort of think there are a couple managers who could maybe make that work weekly).
RB - 25% chance we have a player in the squad who can have a really strong year at RB
We have Dalot is 20 and there's no real reason to think he's ready to play 45 games and have a strong season as a starter next year. 15 games backing up the RB and another 10 at RW, RWB (if we go 3-5-2) and LB and lots of sub appearances would be a fine season for him. I have this below RW only because at Dalot's age and with how highly he's rated, it's at least plausible he has his breakout season like a guy like Alexander-Arnold or Bellerin did, a year or two before one would probably have expected it to happen.
CB - 40% chance we have a player in the squad who can have a really strong year at CB.
Smalling is a very solid if limited player and while right now it seems unlikely Bailly will have a strong season and become a starter, we all liked what we saw of him a couple years back and he will only be 25 next year.
and then we need a midfielder but can survive another year with the current group if nobody leaves, as we have a star in Pogba, a good player we all trust in Herrera and then Fred and Matic are solid, proven players, I'd say 50% chance Pogba and Herrera stay healthy and one of either Fred comes good or Matic has a strong comeback old #6 Thiago Motta at PSG style season, with more rest and a stronger team around him, and I suppose a sliver of a chance McTominay breaks out and passes them with his age and his playing better as of lately.
I can't imagine we won't sign 2 rightsided players and a CB. Even if we strike out on Sancho and De Ligt and a top RB, surely the club would go after some very gettable, more affordable but still productive players hungry for a big move like Ziyech, Pepe, Thorgen Hazard, Neres, Malcolm, Oyarzabal, Lozano/Bergwijn, Bailey, Alderweild, one of the Serie A center backs people seem to rate (Andersen, Manolas has a release clause, Milenkovic), one of the better Ligue 1 right backs (Atal, Lala and Sarr I guess).