I strongly agree with the advice to CO wash - try it you might be surprised.
Strangely, I found that my hair has been getting wavier the older I get. I finally figured out why.
I no longer take the time to blow dry, and use a curling iron like I used to and now that I have adopted the curly girl method I never do. And my hair just keeps getting wavier, these days it spirals easily when wet.
Perhaps your shampoo / mousse combo is killing the natural wave you used to have, and might have again. Seems like it probably is.
Try the curly method for a week and see if you don't notice some improvement. CO washing was probably the single best thing I have done for my hair in years. Oiling would be the next or perhaps no heat. Probably no heat was the next most important, followed by oiling.
As smooth as my hair can get. Thank you Coconut Oil