Happen to be in the business and have probably sold close to 5000 -10000 Aerons over the last 20 years.
The Aeron is probably one of the best if not the best around. I sit in one I bought new manufactured in 1998; almost 20 years ago and have never had to fix anything. Some folks don't like the mesh seat because it can be a bit hard on the pants. If your giving your computer a good work out more than watching TV this chair might be the way to go. The reason the mesh is so popular is because it doesn't cause friction like normal upholstery fabrics do. The mesh creates circulation by letting air filter through and actually lowers your body temp almost 5 to 6 degrees thereby reducing body aches, pains and the associated fatigue. Look for one on CL. Just check the date of the manufacturing sticker on the seat bottom. Anything over 8-10 years old I wouldn't buy; there are lots of newer ones out there for the same money and they come with a warranty. Aerons sell for around $400 to $500 for used fully optioned models. Fully optioned models have two adjustment levers on the left (sitting in the chair) and one on the right. It should also come with an adjustable lumbar cushion on the back side of the seat back. New, I think they are around $800-$900 optioned. I don't feel a stripped version is worth the money. I don't sell Aerons anymore because I'm no longer affiliated with Herman Miller as a dealer.
Another chair to consider if you have a bad back is Allseating's Therapod Chair (made in Canada).
Therapod Therapist Extra Highback | Allseating
It has hidden belts that tighten and loosen back lumbar tension as you need or don't need back support. Watch their video. Its a manual process to adjust, but once set you will rarely change them. I recommend the value plus mechanism, and the grade 3 Moguls fabric; its quilted and further softens the sitting and support to the back. I do sell Therapod chairs and if you want more info shoot me a PM.