1. If you're talking about feeling physically comfortable:
* être à l'aise - This is the most common and direct translation.
* être confortable - This is a more literal translation, but less common.
2. If you're talking about being comfortable with something:
* être à l'aise avec - This means "to be comfortable with" something specific.
* se sentir à l'aise - This means "to feel comfortable" and is a more informal way to say it.
Here are some examples:
* Je suis à l'aise dans ce fauteuil. (I am comfortable in this armchair.)
* Elle est à l'aise avec les enfants. (She is comfortable with children.)
* Il se sent à l'aise dans son nouveau travail. (He feels comfortable in his new job.)
Remember to choose the phrase that best fits the context of your conversation!