Could as well give a chance to Valle instead. Give him another season on loan and see how he develops.
More likely though, contracts of players like Bernat, Acuna, Jonny Otto and Tagliafico (Reguilon, Borna Sosa and our old friend Junior Firpo as well if we're looking at players not already in their thirties) are expiring in 2025 so we could try to get one of them for cheap next year. Ofc some of them will probably change clubs in next 6-12 months though so they could not be available.
Don't think it will happen (especially now that we've signed Inigo as a left-footed CB) and I don't see us spending big on a backup LB so alternative could be a hybrid LCB/LB like Hincapie if he'll still be at Bayer next year. Probably too expensive as we'll have other more urgent needs and still not too much money to spend though. But if Xavi figures out this season he wants to play more with 3 atb then he'd be a great signing imo.
As for this season if we can get Cancelo on loan (very unlikely imo) then he could cover LB too if/when needed. Would definitely play Kounde RB/Cancelo LB over Cancelo RB/Alonso LB.