I've used "a chair".....but not "the chair" ( aka "the electric chair" )
Seriously, I have kept a log and started a meditation practice over 6 years ago. I haven't missed a day in that time. For the first several years I used a chair. I got fantastic results and had some of my best meditations during that time.
Sitting on the floor does add a little bit to the experience, but it is far from essential. It is about what does on in your skull.
The most important things when sitting are to keep you spine straight, but relaxed
and not to be reclining so you stay alert. I've had the best results using a non-cushy, straight backed chair with a cylindrical pad in between the small of my back and the chair. That kind of pad will make it easier to keep your back straight and comfortable. A rolled up cushy towel or a pillow will do too.