Cut Christmas trees really are the way to go. There is no obligation to take care of them after Christmas. They do not need to planted out into a garden that will be too small for them as they grow. They do not need to be maintained in a pot, only to get disfigured or partially defoliated before next Christmas. They simple get removed from the home and composted or otherwise disposed of.
Potted living Christmas trees may seem like a good idea, but they are not as sustainable as they seem to be. Only the smaller and more compact types of conifers can be confined to big pots or planted into compact garden spaces. Rosemary shorn into small cones happens do well either in big pots or out in the garden, and if preferred, can be allowed to assume its natural bushy form.
Many other potted plants that are popularly brought into the home for Christmas decoration are easier to accommodate but take a bit of effort. Poinsettias are the most familiar of these. They can grow as houseplants for years, and might hold their colorful bracts for months. In mild climates, they can be planted in the garden, but will never look like they did originally. Most get discarded.
Hollies and azaleas are more sustainable, but are not as popular. Of these, hollies are the easiest. They can be planted in larger pots or directly into the garden later, when the worst of winter is over. Azaleas will eventually drop their flowers, and will likely look very distressed for a few months, but if watered regularly, can regenerate new foliage that is adapted to their new environments.
Christmas cactus happens to be a delightful houseplant regardless of the season. It will also drop its flowers, but will generate appealing pendulous foliage that cascades nicely from hanging pots. It can bloom annually, although timing of bloom is quite variable. It can do the same outside, if sheltered. Amaryllis also prefers to stay potted. It will replace its tall flower stalks with a few leaves that sustain the bulbs until dormancy next autumn, and can bloom again next winter if given a chance.