I have an office "typist" type chair whcih has a gas lift and is on wheels. Not the lounge executive type. No side arms.
When I sew I do so in stockinged feet resting my heal on the arm of the base of the chair and the ball of my foot on the pedel. I find it reduces leg stress.
The importnat thing is that you are at the right height. your arms should be relaxed and your elbows at right angles. your shoulders shouldn't be too slouched nor to shrugged up.
I like the gas lift because I can change the height depending on if I am using my machine on top or sunk into the bed of my table.
If I go to a demo and will be free machiening all day I take my office chair with me.
best Becks