Amazon and Safari 11.0 no longer work after macOS 10.13.2 upgrade
Introduction
To start with, I can verify that, when viewed in Safari, the content of the Amazon website displays correctly. I am a frequent user (and from your wording of the problem, it sounds like you are too) of their services and have undergone the macOS upgrade (through every version of the High Sierra releases) myself several months ago.
Before or after the upgrade, I have not witnessed any of the problems you describe in the question.

This got me thinking that it is most likely an internet, Safari Settings or Location problem as certain content can only be served under certain conditions, e.g. your physical location.

Analysis
Let's begin to eliminate a couple of things:


As you mention that this has occurred after the macOS upgrade (which brought with it a new version of Safari - 11.0) and all was fine before the upgrade, I am almost certain that your physical location (determined by your IP address) is not to blame.
I doubt it is an internet issue (as it appeared instantly since the upgrade), which could cause the website content (i.e. the scripts that serve you the dynamic content such as Amazon listings) to fail intermittently. Visual feedback of such would include very long load times and frequently unrendered website data.
That leaves us with the Safari Preferences and content blockers you may have enabled. Based on my earlier observation that everything displays as usual when I access the website, I would like you to check your own Safari Preferences: Safari -&gt; Preferences for the following:


Security Tab: Check that Enable JavaScript is checked.
Websites Tab: Go to Content Blocker and remove any Amazon entries from the list. Next, click on  Location and ensure that no Amazon entries are set to deny. If you scroll down in the sidebar on the left (where you also found Content Blocker and Location), you find Plug-ins, uncheck any that you haven't heard of.
Extensions Tab: Ensure that no extensions added by you (such as AdBlock Plus) prevent content on Amazon from loading. Whitelisting Amazon's website is recommended.
Advanced Tab: Select Proxies and ensure that no proxies or VPN tunnels are set, giving Amazon a reason to hinder access.
Privacy Tab: Ensure that Block all cookies is unchecked - Amazon required them.  You can further delete all Amazon cookies in case Cookie corruption occurred.
Go to: Privacy Tab click on Manage Website Data... and use the provided search field in the top right-hand corner to search for amazon then click Remove All. This next time you visit the Amazon website, everything is as though you have never been there before, simply log in again and the data you deleted in the previous step (cookies) will be regenerated. This method may prove to be a key step in solving your problem as cookie corruption (although uncommon) has been known to happen between browser upgrades from time to time.



  Cookies essentially store website information between sessions to
  allow you to get back to where you left off much quicker.



Conclusion
To wrap up, the issue (from what I am gathering) is with your installation of Safari 11. At this time, the latest version is 11.0.2, is this what you have or are there further updates you have not yet installed?
Although I think my answer pretty much covers the essentials, you can read up on resetting Safari if the problem persists. Let me know if that makes sense and definitly how you get on.