I've just finished reading 'Broken Bonds: Surrogate Mothers Speak Out', edited by our very own Spinster @jenniferclahl , Melinda Tankard Reist and Renate Klein. I read it in one sitting. It's mostly the voices of surrogate mothers themselves and is extremely powerful and absolutely heartbreaking. The physical and mental costs to these women is enormous. There is so much hidden knowledge about the process that is shared by these women. It's also very well researched by the editors who are feminist campaigners and additional information is included as well as the reports given by the mothers. I very much recommend it.
https://www.amazon.com/Broken-Bonds-Surrogate-Mothers-Speak/dp/1925581551