A version of the most popular input method for japanese, adapted to latin, seems suitable: the layout is your good ol' feature phone numpad, but instead of tapping 1 2x to input b and 3x to input c, swipe left on that key for b and up to input c instead, etc.
With Latin's smaller alphabet, you can even have the best of both predictive text and precise input: maybe have the plain tap on 1 be a wildcard (a|b|c) for the predictive engine to infer
With Latin's smaller alphabet, you can even have the best of both predictive text and precise input: maybe have the plain tap on 1 be a wildcard (a|b|c) for the predictive engine to infer