Assuming you are well informed about AMP itself, I would go about adding alternative liquid templates (also official docs here) to your current theme which would essentially be AMP versions. Paired with some URL redirects to https://my-store-uri/amp > https://my-store-uri?view=amp_template_name&=1 or similar and you'd be set for most part.
Caveat emptor - haven't tried this myself.
Hope that helps or points you in the right direction!
Nick here from Shopify.
I looked into this for you and found that without a plugin/ app your best course of action to generate an AMP for your Shopify store would be via a Shopify Expert or developer. It is quite a complex and custom feature to add. You can find an expert from the Shopify Expert directory list here. can I also ask why you don't want to generate an AMP via an app here also? Shopify also has a great blog post about this that might be of some value to you also called How Google’s AMP Project is Changing the Mobile Web.
I know you mentioned you wanted to do this without an app. But should the information above change anything for you and you decide to go down the route of an app, the top apps for generating AMP's can be found below:
Hopefully, this helps gives you some direction about how to go about your next step. Any other questions, just let me know.
All the best, Nick
Hope that helps.
All the best, Nick
Is there any reason why AMP-ifying a theme would be impossible without an app? For example via alternate templates, some redirects and rel="amphtml" for mobile clients (possibly forgetting a few more bits and bobs, but you get the gist). I mean, AMP isn't really any magic requiring apps if you are able to code some Liquid. Just wondering.
Great question. I did some digging and spoke to a higher technical theme support team about this for you. It's certainly not impossible but it would require a LOT of redesign and not an easy job by any means. Unless you are someone who is very skilled and have the ability to do this, we'd probably advise against it, in the chance, it could disrupt other aspects of the code in the backend. It also explains why there are several good apps in the app store for the same functionality.
I hope that answers your question.
For what it's worth, anyone who comes here wondering about AMP without apps, it is, like @Nick mentioned, an endavour for developers with a good understanding of web technolgies, AMP, Shopify platform and SDK/API's + Liquid who are on a tight budget or control freaks who'd rather avoid 3rd party apps if possible ;-)