I'm in the process of training my left foot as well. It helps for me to do singles and doubles at slow tempos, gradually increasing the speed. Before increasing, it's important to be able to do those singles and doubles at constant for an extended period of time, say 2-5 mins. Some may disagree. Once you build that consistency, then increase the tempo.
Paradiddles are tough but can be done with enough patience. I do the Thomas Lang method. Heel up for the first note, and heel down for the last 3 notes. It's about using dynamics for this. I also do singles, doubles, triples, and paradiddles on the snare while doing singles and doubles on bass, hoping to help my independence.
Let me know if any of this works for you. Also, check out previous posts. A lot of great info has been given regarding this subject.