Johann Baptist Cramer's Op. 14 sonatas are excellent examples of the late Classical style, balancing technical challenges with expressive musicality. They are pedagogical in nature, developing fundamental piano technique.
Requires developing finger strength and evenness for rapid scalar passages and arpeggios.
3 Sonatas (Op.14) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
3 Sonatas (Op.14) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.