Ive had the same problem earlier on...I suggest using Godowosky's left hand etudes of Chopin..Even if you don't want to master them to perform, its a GREAT exercise for the left hand and helps it get even with the right hand. Godowosky himself said that both hands should be equal, so it would be a good project for you to work on, and who knows, maybe you could even master them to perform! I suggest starting with the Opus 25 no 12, C minor etude, transposed to C sharp minor for the left hand.
Richard