Thanks lorax. Personally I often do searches on my smartphone and then move to my laptop to place the order because it's just easier and quicker to do it that way. My gut feeling is most people do that, in which case there's nothing to be gained by having a bespoke mobile site - my overall conversion rate will be the same regardless.
I also prefer using the full version of a site as I want the full features and I won't usually search for something on my mobile if I don't have 3G or wifi access because it's just too painful.
I just read an article comment that advised adding PayPal to improve conversions as it saves people entering lots of details, but now I'm wondering if it might just be better focusing all our effort on making our site really quick and easy to use for everyone.