Any tips on spicing up a piano song with just four chords on the left hand?

I'm writing a piano song using 4 chords with the left hand - F#Minor, A, C#Minor, B.

The song starts off with just the chords and the right hand plays a melody in E Major. 4 measures in, the chords switch to arpeggios (using the same 4 chords above) to add a little flavor, while the right hand continues playing melodies in E Minor.

It sounds nice, but as the song progresses into a minute or two, the left hand continues arpeggios using the same 4 chords and this starts to feel somewhat repetitive.

I don't want to change anything about the right hand as I'm set on that/set on the E Major scale, but I'm just wondering if there are some chords that will match what I've written with the right hand but are different than the four chords I've been playing so that it's not so dull.

I know basic music theory, but not enough to know chords beyond the basic majors and minors to help me in situations like this.

Thanks!