Minimize the change if possible. As the heater dries the air, you must attempt to re-humidify it. That may just involve putting many other houseplants near the Ficus . As long as it responds with healthy new growth that persists, your Ficus is probably healthy and much less worried than you. There are many plants that do well on windowsills.
Herbs are a good plant for the window garden.
They can be attractive, fragrant when brushed, and useful in cooking. Some even have attractive flowers. Chives, bunching onions, basil, marjoram, oregano, cilantro and many other herbs are good choices. There is no shortage of flowering plants for the windowsill. Vegetables are somewhat more difficult to grow in the window, but recently nurseries have begun offering miniature vegetables for the window gardener.