Traditional is what you make it at the end of the day, but green and red is the classic theme, and in late December your suitable plant options are limited.
Only evergreens are in leaf, and few plants are flowering in the house or in the garden; florists can source flowers from greenhouses.

Norway Spruce is cheap and does drop needles before long unless it’s outside, Nordman Fir are dearer and do not drop needles even in the warmest house.
Those two became more popular than the native Scot’s Pine, which you still see used for door wreathes.

List of Christmas Plants

• Holly
• Ivy
• Oak
• Cranberry
• Red Roses (from a florist or hothouse, as flowers in December)
• Radish
• Cyclamen
• Mistletoe
• Poinsettia
• Cinnamon bark
• Ginger
• Pomegranate
• Azalea
• Cymbidium Orchids
• Christmas Cactus (Schlumbergera)
• Amaryllis belladonna
• Helleborus niger