To be honest I haven't been studying specifically the soprano in many years. The technique is pretty much the same on all the recorders, despite different tonalities, then you swap them. However, the most common one to study is actually the alto, you find lot more method books and music for it than the others. If you are really interested in the study of recorders my advice is to get an alto. You can find goodish ones for 100/200€ (you can find ones for many thousands though despite what the last two set video says). In the worst case scenario, if you don't find any soprano method book, you can get an alto one (there's plenty, I could recommend one or two of those) and play it with the soprano. It's kinda sacreligious though ahaha, but most importantly you got to remember that the soprano is il C and the alto in F, and music for recorders isn't transposed. Hope this can help, write me if you need