I forgot what you play… but most arrangers got a feature that adds a block chord around your solo line based on the chord the LH plays. On Roland’s it is called Melody Intelligence, on Yamaha’s it’s called Harmony/Echo, I think. But they offer a variety of types of chord voicings (like block same sound, block with a second sound, duo, trio, four voice etc.) and one of the types in Roland’s at least is to simply double your one note melody with a note one octave or two octaves below it.

If you want an easy way to make your single note solo more powerful, and can’t play well in octaves (tough with just one hand!) it is an easy way to make it sound bigger…