Kate, wasn’t the weather lovely last November!
I am close to being in the same position and like you am amazed at the slow growth of new plantings, which normally race away at this time of year, with full light and reasonable warmth. I think some of the problem is continual rain keeping soil cold and relatively airless. No remedy except I have wondered about putting a winter cloche on one bed at least. My young lettuce are covered with fleece but it is not helping a lot. As long as slugs hold off they will grow in the end but meanwhile we lose customers (temporaily I suspect) and income. Apart from some dark, deep freezes in midwinter, I have managed nine years without a break until this!
One bright spot is some nice sweet basil in the tunnel!