How can I keep my small garden looking nice during fall & winter?

Synethia, I would make some visits to local nurseries and ask for recommendations.

https://pender.ces.ncsu.edu/2012/10/plant-flowers-and-veggies-for-winter-color/

https://www.bhg.com/gardening/flowers/annuals/winter-flowers/

http://www.costafarms.com/get-growing/slideshow/12-annual-flowers-that-can-take-the-cold

https://timesofindia.indiatimes.com/life-style/home-garden/six-easy-maintenance-plants-you-can-grow-in-winter/articleshow/50636568.cms

You could add in some mums bring in some fresh mulch and perhaps do some simple planters to mix in with fall pansies and such. Check what the nurseries have in stock right now and then to enjoy in bloom during freezing temps you'll have to cover at night.

Last year we planted petunias and added some fresh mulch. The petunias stayed looked decent and even bounced back after being covered in a few feet of snow! (We're in Maryland)

Chrysanthemums. they come in many colours and flower shapes.