I still disagree with Majin Boo being a main inspiration for Big mom's entire character and only because her relationship with Tama is reminiscent to Boo doesn't mean that he served as an inspiration as a whole, especially when Weevil and miss bucking are an exact copy of Boo/Babidi.
Big mom's main inspiration was quite obviously Yubaba from the movie "Spirited away", at least to me. Some of her abilities even manage and the design is a dead give away.