Failing that, Hive are, in my opinion, the best place to buy books (plus DVDs, Blu-rays, etc.) online. Hive donate a proportion of all their sales to independent bookshops. After any purchase you make, you can select which bookshop that donation goes to.
Over the years I have found Hive to be consistently cheaper than the behemoth, bad-employer, poor tax-paying Amazon. If that’s not enough, once you’ve chosen the book you want on Hive, they do NOT add delivery charges: that’s free.
(I am not signed up to Hive’s affiliate program, so get nothing from this plug.)