Elizabeth of York dies in a childbirth a few years earlier. Isabel, Princess of Asturias becomes Henry VII's second wife. Barriers are Prince Arthur's engagement to Isabel's little sister Catherine of Aragon.
Or alternatively make Richard III survive and marry Isabel. In the OTL, Ferdinand and Isabella did float the match. Richard III's first choice bride Joan of Portugal dies of an illness.
Charles VIII of France (born in 1470). Avoid Edward IV going to war with France and the subsequent betrothal of EoY to Charles VIII (which was broken). Might have to play around with history a bit to make it happen. But perhaps the marriage is used as a settlement with France and Ferdinand.
Francis Phoebus (born in 1469) is also a good option.
I vaguely recall reading somewhere that Ferdinand & Isabella actually considered Isabel for Ferrante of Naples (who later married his aunt, Giovanna) and another daughter for Francis Phoebus, but in both cases the marriages were dependent on either prince holding their throne in the face of French aggression. Would these be good matches or simply alliances of convenience that would be thrown aside once no longer required.
Isabel can marry Prince Filiberto of Savoy, the son of Amadeus IX, Duke of Savoy and Yolande of Valois. Yolande was the sister of King Louis XI of France.
With Isabel marrying Filiberto, ties with France are strengthened.