Johann Baptist Cramer's Op. 35 sonatas are well-crafted pieces that exemplify the clarity and elegance of the Classical style. They often feature pleasing melodies and well-defined harmonic progressions.
Requires attention to evenness of touch and a sensitive dynamic range.
3 Piano Sonatas (Op.35) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 6.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
3 Piano Sonatas (Op.35) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.