I recently did some testing like you did. Good idea.
Basswood apparently behave like Pine. You can get them from any construction site.
Your neck look like maple on maple. Maple is harder to find and expensive. I somehow secured some offcuts to test on but the local timber supplier suggested some meranti for a similar hardness. It’ll be. A different colour though.
Alternatively you can shape the headstock then use the offcuts from the headstock.