Its just not that simple; its the weapon systems and sensor integration that costs the big £ and that would all have to be new.
TBH, we might be better off with a few "Oceans", with a strengthened flight deck. Run the GR7/9 off them, along with Merlin. IIRC the Ocean cost the same to procure as a single T23. Once GR7/9 dies then i'm afraid its back to the LPH role, with the possible addition of a TLAM type weapon & a maritime UAV?
Its a long way from ideal, but then we are financially screwed and needs must. Still keeps a few people in jobs, too.