Paul Barbot’s Op. 109 is a characteristic minor-key miniature focused on evoking a sense of loss and retrospection. The harmonic structure is relatively straightforward, allowing the performer to focus on nuances of touch and tone color.
Develop a subtle use of rubato to enhance the contemplative character of the piece.
Comparable difficulty and character — good candidates for what to learn next.
Bonheur perdu (Op.109) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
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.
A typical performance of Bonheur perdu (Op.109) lasts about 3 minutes.
Bonheur perdu (Op.109) 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 Berceuse Triste by Alfredo Casella, Berceuse Triste by Alfredo Casella, 'k Hou van stilte by Peter Leys — see the full similar-pieces list on this page.