Well, I guess I should tout the app I develop Certify The Web: https://certifytheweb.com/home/features
There are several fine command line and scripting based solutions as you will already have seen but I’m pretty confident we’re the best GUI for ACME/Let’s Encrypt currently in existence (although I’m obviously biased as the author). The source is available on GitHub, it has free and paid versions and it’s my full-time job so there’s commercial support for companies that want it. In turn we sponsor some of the other ACME clients, because we’re all in it together!
There are many bundled DNS providers (some of which are via Posh-ACME, but route53 is native), there are also many bundled Deployment Tasks and IIS etc is a built in target that the UI has been optimized for.
For simple IIS stuff the process is click New Certificate > Select IIS Site > Request Certificate and everything then works automatically and it adds/update https bindings etc as required. It can do a whole lot more than that, but that’s the basics. Questions etc here: https://community.certifytheweb.com/
CTW was first established in late 2015 and is now used by hundreds of thousands of organisations around the world.