Studies for development

[colette]

I am a faily advanced pianist, I can play some pieces Rachmaninov, Chopin and Liszt. Though I practice technical exercises, scales, arpeggios and broken chords, I have never learned any studies. I have considered starting on the Chopin Opus 10 studies, but I'm not sure if that would be a good place to start. I have also considered learning the Bach Two Part Inventions as studies, I read somewhere that his 15 pieces were written for the purpose of teaching. I suppose I am looking for studies that have much more to them than mechanical difficulty, and that are not astronomically difficult to play. Any suggestions please?