Indeed, sedentarism can cause many illnesses and lead to an unhealthy lifestyle! It is very good that you have realized how bad it can make you an unhealthy lifestyle and try to change something. You can start with lighter things in the beginning such as genoflexions, jumping on the ground, gymnastics or even dancing. It's important to do daily at least a few minutes until it becomes a habit. At first it will be difficult, but after the first few weeks you will notice an improvement in your physical and mental state that will motivate you to continue! Good luck!