Many people can recognize the classic lotus pose, however you don’t have to be able to sit like this in order to practice breathwork.
Most important when practicing breathing exercises: make sure you feel comfortable and safe. Some practices will invite you to sit down, others will ask you to lie comfortably on the floor. Simply follow the instructions of your teacher, he or she will always explain what the most ideal position is for the particular session.
That being said, to allow full, deep and diaphragmatic breaths, you can follow these basic guidelines: keep your spine straight, shoulders down and away from your ears, body relaxed, eyes closed and chin slightly tucked in.
If you find a particular position to be painful or uncomfortable, always listen to your body and adjust if needed. The most important thing is that you can sit or lie comfortably during the length of time of your session of choice.
To make yourself extra comfortable while practicing, it is always perfectly fine to use attributes such as a blanket to keep you warm or a meditation pillow to sit on if that helps you during your practice.