Just a thought on the office chair - I think one with arms would be safer - and more comfortable.

Believe it or not, I found my current one (with arms) by the side of the road during a council clean-up. Someone had thrown it out because the lifting mechanism wasn't working, but when I tried it out, I found it was exactly the right height for me, and extremely comfortable - just like it was made for me - in fact it's the most comfortable chair in the house. Just as well considering the amount of time I spend on Mudcat!