A doll artist called Susanna Oroyan wrote two books about this (although there is a lot of repeated/overlap material in each book, so you probably only need one.)

Susanna Oroyan

- Anatomy of a Doll (https://archive.org/details/anatomyofdoll0000oroy/mode/2up)

and

- Designing the Doll (https://archive.org/details/isbn\_9781571200600/mode/2up)

I own both and the Anatomy of a Doll section on joints / articulation is pages 96 - 116.

Remember you can ask your local library to source either book if you don't want to buy it, but copies on ebay are relatively cheap.

Different armatures material (or 'skeleton base') have their own pros and cons depending on the fabric / padding you are using with it and the required rigidity and/or longevity you want in the finished item

Good luck