I'd go for something you can grow in a big pot, Nantes Frubund as mentioned above seems successful or Amsteradm Forcing 9or similar round carrots like Rondo).... I've got som eI put in pots a few weeks ago so that I could bring them in (Eskimo and Nantes) but I've also planted out some Autumn Giants. I've found that carrots are perfectly possible to start in modules, 24 to t atray with a toilet roll pushed into the top of it, they can be sown up to six weeks before the space becomes free making it possible to follow potatoes, peas or broad beans quite easily with a maincrop carrot...