AbeBooks is this rich and vast online store that has tons and tons of stunning books for kids and adults alike. They may not be cheap, but they are awesome and the company now offers both free standard postage within the UK and free worldwide postage too.
The way their system works is a little different from the norm so you’ll need to visit the free delivery page first and then choose your titles. You search for eligible books using the form at the centre of the page and then, when you have chosen the titles that work for you, you proceed to the checkout which is where the discount will be applied.
You can search for author or title or keyword or ISBN or you can use the More Search Options tool to fine tune your search even more. At the bottom of the page is a listing of popular titles with free postage that’s pretty extensive if you fancy looking there first.