I am not sure if this is the best forum or if it should have been under Accessibility & Usability instead. Apologies in advance if I made the wrong choice. 
The situation is this: I’ve got a site (www.westeros.org) that’s been around for quite some time and design-wise it isn’t the most modern. In particular, it is probably wildly unsuitable for mobile devices and given the amount of mobile traffic the site is now getting, I really need to look at what can be done.
A full redesign isn’t on the table at the moment, but what I am trying to figure out is what the best approach for creating a mobile alternative would be. Google Adsense has been sending along various tips about going mobile for the last few months and looking over their guides, they suggest three approaches to going mobile: separate site, responsive design and dynamic serving. A separate site is not an option, so its between response design or dynamic serving.
Now, I am thinking that getting my current design to be responsive (especially as I wouldn’t want any major changes to how the site currently looks on non-mobile devices) would be pretty difficult. However, I would be very interested in hearing if anyone has a different opinion on that.
Dynamic serving…well, I am not strictly certain how that differs from a completely separate site, since it sounds as if that would be needed to serve up an appropriate page for a particular device. Or am I misunderstanding? We’ve also run into some issues already with identifying devices on our forum (since that one at least comes with a built-in mobile skin) due to the fact that we’re running Varnish, so that may rule out dynamic serving.
Anyway, as I am sure is obvious from this, this is very much unknown territory for me and I am finding it hard to identify a good point to start from (other than ruling out the approaches that probably won’t work). So, I would be very grateful for any and all advice.