I love fresh cauliflower, but it's so terribly temperature / light sensitive that I might as well just pick it all and freeze it if I actually want to eat it.
Is there anything I can do to ensure Cauliflower stays good in the garden for at least two or three weeks - or is it necessary that I just pick it all at once when it looks delicious, even if the heads aren't as big as I'd like?
This doesn't help you now, and I don't grow cauliflower so I'm not sure if there are problems with succession planting cauliflower, but next year instead of planting it out all at once, stagger your plantings so that you can expect to have as many heads as you want per week maturing instead of all of them maturing at once.
I do this with lettuce, cabbage, and carrots with good results.
I stagger the seeding.
For example, with cabbage (Gonzales, a short-season, 66 day variety that holds well), I start a batch inside in early spring, let them grow under the lights about 6 weeks, then plant out. Then about a week or two later I direct-seed some more in the garden. The heads hold long enough -- and I start harvesting one or two small heads early -- that we have cabbage for a few weeks, then a gap, and then more cabbage. In July (I've got tiny seedlings behind me right now) I'll start a batch indoors for fall harvest.
It occurs to me now that I should also mention holding as something to look for in your variety selection. I don't grow cauliflower so I don't know if this is a consideration, but lettuce and cabbage varities (and other vegs too) will be described in catalogs as "holds well" or "stores well". These will keep in the field or the fridge, respectively, without spoiling.
A combination of variety selection and succession planting may help you extend your harvest.