I am an intermediate pianist working on thebllike yourself.
One thing I find effective to get the left hand improvising is taking three simple left hand patterns A, B,C, then integrate them over the twelve bars. First play the A all the way trhrough, then the B, then the C. When comfortable play ABABABABABAB or soemthing similar, then ACACACACACAC then BCBC etc.. as ideas occur incliude them but only after you are secure with all three paterns.
Well its working for me but bear in mind I am a learner.

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