You can get acid-free archival bags here.

Here is a link to some basic book preservation best-practices just as a refresher. One of the really cool things about archivists and preservation specialists is that they want spread best practices as far and as wide as they can so if you want more specific information on anything its very likely available.

I've worked in archives with large book collections in the past and the polyester bags aren't really ever used for them. For damaged books with loose sheets archival boxes are preferred. I think the best way to preserve a book collection like yours is just the basics for books: storing like sizes on shelves, making sure the books on the shelf are not leaning but not super tightly packed either, keep it out of rooms that are really bright or really humid, make sure there's no inserts or fasteners, and don't handle them all that much.

If they are thick enough that they can support themselves, I don't know if the bag and board is necessary. But I also don't know if it would hurt. Though obviously bagging and separating anything that is already moldy/mildewy is appropriate.

Unfortunately that kind of mass market 1950s-1980s are some of the hardest to preserve, particularly because they started using really high acid paper so the paper just gets more and more fragile until it falls apart.

I sometime see older mass market paperbacks in little versions of the comic bags. I don't know where to buy them though.

Donate them to a museum. Most public museums will allow family access to donated items for viewing. Not sure if you can retrieve the items permanently at a later date if you wish.

My family were wainwrights and coach builders and we donated a full workshop of tools to a Cobb and Co museum and, on request we have taken younger generations up to go through the different items and talk with an expert about their heritage. There’s even a working workshop there where they can see how different tools could be used. They do restorations and maintenance old working coaches and teach that as a set of trade skills still. It’s pretty cool.

Go on Amazon and search "book preservation sleeve". Or if you don't like Amazon just google them. They are out there and in all different sizes.

Gaylord Archival (gaylord.com, I just checked to make sure I wasn't sending you to some dark corner of the internet) has preservation materials for just about anything you'd care to preserve.

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