Chair size
To be comfortable, a chair needs to give you support where you need it, and be just the right size for you. It's fairly easy to tell if a chair is the right size, though you might need to sit in it for at least an hour to be really sure.
Bariatric riser recliner - for heavier users
In the right chair:
You should be able to sit with your bottom right at the back of the seat and your feet flat on the floor.
Your thighs should be level and your lower legs straight up and down.
You should be able to get two fingers between your knees and the front of the seat.
The seat should be wide enough to fit you, but not so wide that it doesn't give you any sideways support.
If the chair has arm rests, you should be able to sit between them with enough room to get your hand in on each side.