You could get some wood and throw something basic together yourself.
That way it would be the exact dimensions that fit your requirements.
It doesn't have to be fancy carpentry or especially strong.
As for seating, I found a great chair on Craigslist for $50 delivered.
It has a lot of arm adjustments and it doesn't squeak if I move.
I'm very comfortable in my studio and also do my editing from the same spot.
I just remove my headphones and use a monitor for editing.