Once you get to around grade 7 level, you can start to look at early classical concertos.
There have been several threads on this subject in the past and indeed the Haydn does seem to be a popular first choice, but there are several alternatives from the likes of Abel, Arne, Avison, JC & WF Bach, Burgess, Clementi, Benda, Chilcot, Galuppi, Giordani, Dittersdorf, Hoffmeister, Hook, Kozeluch, Nichelmann, Paisiello, Paradis and gawd knows how many others. Many are on IMSLP and some still exist in modern editions.
A whole World will begin to open up before you as your powers increase.
Thal