Wavelet signal analysis for ultrasound echo
From what I can see you are not trying to detect defects. For defect detection  (CM,Inspection) wavelets are really popular and they had and still has been used extensively. I am working in the same field for a while but from what I can understand, you are trying to measure the thickness of the material.

In any case, I couldnt quite understand your problem but I strongly advise you to go for spectrogram first. Scalogram is inherently better in terms of resolution (both in time and frequency) but it might be a bit tricky to understand scale-frequency relation as opposed to spectrogram. 

Based on your plots, wavelet transform is picking up quite a few of wavelets. This probably is due to the fact that your signals are overlayed. You might want to seperate them. You might also want to go for different wavelets and decomposition levels, I personally know mexican hat and db mother wavelets can provide good results for NDT applications, both for denoising and transforms.