Saddle chairs with armrest come whether with one or two pieces attached to the sides of the chair where you can lean your elbows and rest the whole arm.
As with the footrest, the elbow supports might be attached fixed or adjustable. When it is only one, some brands hold it on the lift cylinder and it can rotate around the chair almost 360 degrees. Contrary, when they are two, the rotation joints are on both sides of the chair and they rotate within a limited range.
These chairs can have higher prices than others because in addition to the elbow support a backrest is usually added. Although, you are not going to regret since the use of the supports helps more to reduce shoulder and neck strain and adds comfort while working on a daily basis.