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If you are in zone 5 or higher (learn your zone here: https://www.gardeningknowhow.com/planting-zones/usda-planting-zone-map.htm )the plant should be fine in winter. Hopefully you have a variety that is hardy in your area. If you wish to keep it in the pot, you could dig a hole and sink the plant and pot into it; that way, the earth will insulate the roots from killing cold. Cover the whole thing with mulch, as you would for plants in a bed. This article has more information that you should find useful: https://www.gardeningknowhow.com/ornamental/bulbs/crocosmia/crocosmia-bulb-care.htm

There are a number of trellis options available at any local hardware store, nursery or DIY store -- pick a design that will allow your Crocosmia to easily lean against it without getting in the way of the blooms. You can gently tie the stems to the trellis structure as close to the bottom of the plants as possible.

Fencing, bamboo poles, antique ladders...almost anything can be used. Get in touch with your creative side and have some fun when choosing a trellis structure for your Crocosmia!

Here are some additional tips on growing and care for Crocosmia: https://www.gardeningknowhow.com/ornamental/bulbs/crocosmia/crocosmia-bulb-care.htm

Healthy Crocosmin bulbs will bloom midsummer thru early fall but need optimum growing conditions.
Dead head the flowers if your cutting them for cut flowers.
Here is a link to refresh you on the care and growing requirements.

https://www.gardeningknowhow.com/ornamental/bulbs/crocosmia/crocosmia-bulb-care.htm

There could be a few reasons for the poor growth and lack of flowering.
Make sure the plants are properly watered. In warm weather a container may need to be watered twice a day.
Make sure the excess water is draining from the pot.
You may need to move the container to a morning sun and afternoon shade location so that the pot does not heat up so much during the warmest part of the day.
The plant could need to be divided, when flowering slows down it can be sign that the plant is overcrowded.
Look for signs of disease or pests, do the leaves yellow then turn brown?
These links will help refresh you on the care and help you pinpoint the cause of the issues.

https://www.gardeningknowhow.com/ornamental/bulbs/crocosmia/crocosmia-bulb-care.htm

https://www.gardeningknowhow.com/ornamental/bulbs/crocosmia/problems-with-crocosmia.htm

The plants could have been suffering from transplant shock, a common problem. They will probably come back next year after they recover. Since they are not actively growing now, don't fertilize any more, and water only once they dry out.

https://www.gardeningknowhow.com/houseplants/hpgen/repotting-stress-treatment.htm
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

You can cut back the seed heads and stalks, but it is best not to cut back the leaves until they die on their own at the end of the growing season. The plant needs them to store energy for growing and blooming next year.