Pretty much anything will look great with that - it’s a lovely ring. Personally I love mixing metals so think a rich high-karat yellow gold band in the same width as the shank on your ering would look amazing, pipe-cut for a slight point of difference.
I'm a matchy-matchy wedding set person (I like things to look like they were designed to go together), so I would get a diamond half-eternity band to match the band on your engagement ring. It is a beautiful ring! Congratulations.