Back to the question:
What do I choose, if I don't like an extension and I don't like an additional string, but want to stay with a "standard" 4 string bass ?
If I really need a lower node, I would prefer retuning the bass. Tune down the E string to D for a song, if that is needed sometimes or else retune in quints, if I think a wider range is necessarry for the instrument.
Extensions look ugly and are difficult to play fast, an additional lower string makes the room between strings smaller and damps the instrument.