Please help me choose an office chair.

Hi everyone,
I’d like your advice on buying an office chair. My problem is that I’m (quite) overweight and that I have to sit long hours in front of my PC. It’s an important part of my life: I sit at my desk for work and for fun. All in all, perhaps I spend over half my time in my office chair.
Because of these two factors combined (weight and long hours) I’m actually beginning to have health problems. Basically my weight destroys my nether regions. So much so that I had to see a few doctors lately.
Thus I decided to get myself a really good office chair. Not quite the very best, but close enough (I hope). In other words, I’m not ready yet to dish out for an Aeron, but I do have a mind to buy a Mirra.
I also had the chance to try a SteelCase recently (I believe it was a “Please” but I’m not sure.) I rather liked it.
So, what would you recommend given my situation and budget? Is there anything better than a Mirra in the same price range?
A big part of my problem is that I can not try a particular model. I can’t try anything. I live in France and my acquisition would have to be made by mail.
Any pertinent info is appreciated. Thanks.

Check out Sitmatic. They are super configurable and they have options for “oddly sized” folks. I personally got a wide chair with arms, myself.

How much room between arms do you need?

No more than any regular guy. Larger would be better, but usually I have no problem fitting in chairs wherever I go (except perhaps for some airlines). It’s mostly the weight that’s causing the problem.