Good to hear you survived some of our "cool" weather. I was out in some of that myself for 4 or 5 days this last week. Great fishing, but chilly when you are still crunching through ice on the shore at noon!
My floor is definitely a cold spot too. I am still debating on insulating from underneath, or going with some of the foam "puzzle" mat. http://www.homedepot.com/s/foam%2520flooring?NCNI-5
I might end up doing a bit of both. The only thing I am concerned about with the flooring is dirt getting down in the mat cracks and having to pull it up frequently to get it out.