What would be the best way to setup a mobile theme for an existing domain with domain access module? We have implemented a multidomain portal using domain access module. Now we would like to setup a mobile site for each domain added. 

Initially we thought about going for responsive layout, but as the mobile portal has very simple layout with minimum elements, using responsive model might be an overkill as it load every html elements to mobile even if most of the elements are not used in mobile theme. Also there are few features/blocks like slider etc implemented differently in mobile theme.

The m.domain and separate theme for mobile site looks like a feasible solution. But I am not sure what would be the best way to integrate it with domain access.

We want all content in the desktop domain available in the mobile domain, only theme need to be changed. It would be good if we were able to setup a domain alias where we can provide the m.domain.com in the configuration for the main domain and use the same access control as main domain, only change will be the theme and the links rel="alternate" and rel="canonical"

Also we need to setup a http redirection when a user visit the site from a mobile device. (Any suggestion for switching back to the desktop theme from mobile device and vice versa)

Is there any way to implement something like this using domain access?
You need these two modules to do this:

https://www.drupal.org/project/simple_mobile_redirect
(detects mobiles and redirects them to pre configured paths)
&amp;

https://www.drupal.org/project/themekey
(serves any theme (e.g. a customized mobile theme) under any pre configured path)