Choosing decomposition level discrete wavelet transform

I have som issues with wavelets (DWT). I am stuck at choosing proper decomposition level and mother wavelet based on entropy criteria. I've decomposed my electricity load signal via

lvl = log2(length(N)) %where N - signal,

and obtained max level of decomposition, then I performed wavedec at max level and obtained Appx and Det coefficients. Now I want to compute entropy of each subband so I have to compute entropy at each level from A1 to Ai or entropy of reconstructed signal? When I compute entropy how to select which one is the proper decomposition level? It would be helpfull if someone could help me or atleast explain me steps. Looking forward for your help!

Matt