Several things make comfort

Seat

1. Height from floor to top of cushion. Since people come in varying height, the comfortable seat height varies with each individual
2. Seat compression. The amount of Seat Compression depends upon the type of frame, springs, and support structure the furniture has.
3. Seat incline. Is the top of the cushion flat, or does it slant down in the back?

Backrest

1. Height of backrest
2. Slant
3. Shape
4. compression

Arms

1. Height
   1. from floor to top
   2. from top of seat to top of arm
2. Front to back depth
3. Width of arm