Naked at Lunch has a fair bit of history in it. Not as academic as "Naked: A Cultural History...".
There are numerous resources out there that explain the ins and outs of nudism and this curious desire to run around naked. aanr.com bareoaks.ca bn.org.uk are some places to start. There are also several books on nudism available on Amazon. You might try "Naked at Lunch" (currently only $3.00 for the Kindle edition! Buy it!). If you are a Christian or have some religious leanings, there are several books exploring social nudity from a Christian perspective that I can recommend.
One of the things you may be bumping up against is the "Why would anyone want to do that?" attitude. Part of your challenge will be convincing your wife that millions of people around the world enjoy going to the beach, resorts, and relaxing without clothing. _You_ are unlikely to be able to do that. Bring in some outside sources - such as the book above - to help her see you are not just a crazy person. (Or maybe she'll still think you are, but she'll know there are a LOT of other crazy people, too.)