Henry Eymieu’s Op. 115 Cantabile is a sophisticated late-Romantic character piece designed to showcase a player's tonal control. It features more chromaticism than earlier, simpler cantabile works.
The technical difficulty involves balancing complex internal voices while sustaining a long-breathed, expressive melody.
Comparable difficulty and character — good candidates for what to learn next.
Cantabile (Op.115) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
Cantabile (Op.115) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Ballade by Amy Marcy Beach, Canto del esclavo by Nicolás Ruiz Espadero, Allegro appassionato by Alexander Scriabin — see the full similar-pieces list on this page.