I don't know how big the book you think i am talking about is going to be, hell there are books of just 15 pages-20 pages, those books are very small, but are less vulnerable to damage than a single sheet of paper, i can keep books of these small number of pages in almost every place you just mentioned and it will damage way slower than a piece of paper, i can write my seed phrase in the middle of the book for example, it has an external cover and extra pages, and it will take more time for any agent of damage to get to the very page that contains the seed phrase.

But what about just a single sheet of paper, it will aparently damage faster than my choice. 'In the wall', 'between woods', 'under the carpet', 'in the roof', etc, there are many things that can easily destroy a piece of paper in almost all these places you metioned, they are interesting choices but with cons too that you did not include, agents of damage such as light, humidity, water, insects, dust and so much more, can damage that paper very fast. I do not know where you live, but rats are another thing to look out for where i stay, these tiny rats can be found in surprising places, all of this agents of damage will destroy a single piece of paper faster than a book, the type of book i mean is in the first part of my post, that is why i think it is safer o_e_l_e_o.