Amazon, in their wisdom (!), gave two totally different things the same name ie. individual. We have been complaining about this for years as so many new sellers do not understand the difference.
There is the Individual seller account (the legal entity) where you can ONLY sell off your own second-hand, used items, and not new items, and then there is the Individual selling Plan, which you say you have, as do not pay the £30 a month fee.
Yes, you can sell new items on the individual PLAN, but not with the Individual Seller ACCOUNT.......but as you are presumably selling your book for profit you DO need to be registered with HMRC as self-employed, as explained in my previous post.
I am guessing that your verification went through quite quickly ? - if you only applied for the Individual seller ACCOUNT. Setting up a Business Seller account takes longer as they have to verify your business info as well as your personal ID info. What did you have to supply for verification - if they only asked for personal ID details (bank, utility bill etc, then you do not have a BUSINESS seller account.
You do NOT have to be VAT registered, but you DO have to be registered with HMRC to sell for profit - as you say there is no VAT on books.