Bougainvillea most likely won't make it through your winter season even if covered with a blanket. In a mild winter with a deep mulch and a cover over the top after the first frost it could survive, but that is the exception not the norm. I would dig and repot it as soon as possible. Don't overwater it in the pot. The plant won't like being dug but it's your only option for keeping it alive.
For cool season color you are limited to ornamental cabbage and kale, as well as pansies and violas as the most dependable. Alyssum, stock, and calendula are okay until the hard freezes arrive.
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