I've owned five budget ergonomic chairs in the last six years. Every single one had the same problem. Not the lumbar support, not the armrests, not the recline. The seat depth.
You see, everyone talks about lumbar support and adjustable arms. But if the seat pan is too deep, your back never touches the backrest properly. You end up perching on the front edge. That's not ergonomic, that's a barstool with wheels.
I'm 5'10" with a thigh length of about 20 inches. Most budget chairs come with a fixed 19-20 inch seat depth. That's fine, barely. But my wife is 5'3", and her thigh length is 17 inches. On the same chair, she's got three inches of pan pressing behind her knees. She sits cross-legged or with a pillow behind her back. Meanwhile, the chair's lumbar support hits her mid-shoulder blade.
I see people blame the lumbar support when the real issue is seat depth. They buy a chair like the Oline Ergopro and complain about the lumbar hump, but if the seat were shorter, their pelvis would sit further back and the curve would land where it's supposed to. The Oline Ergopro Ergonomic Office Chair Has a Lumbar Problem Nobody explains this in more detail.
So before you buy any budget chair, measure your thigh length. Sit on a flat surface, feet on the floor, knees at 90 degrees. Measure from the back of your butt to the back of your knee. That's your max seat depth. Then subtract one to two inches for clearance. You want the seat pan to be that number, or adjustable.
Some chairs offer a sliding seat. Usually in the $300+ range, but I've seen a few under $200. If you can't find one, look for a chair with a shorter seat depth, around 17-18 inches. My wife now has a chair with a 17.5" seat, and it's a huge difference.
Also, check the seat width. I'm a bigger guy, 42" hips, and a 20" wide seat feels narrow after a few hours. Look for 21" or more if you're wider.
Another mistake: ignoring the seat foam density. Budget chairs often use foam that compresses within a year. I weigh 220 lbs, and my last chair's seat foam bottomed out in nine months. By then, I was sitting on a solid base. I ended up adding a 2-inch foam topper, which raised me too high and messed with my leg angle. Not fun.
So what should you do? Set a budget, but don't just filter by price. Look for a chair with adjustable seat depth, or a shorter fixed depth if you're under 5'8". Check the foam weight (density), not just the thickness. And don't ignore the seat width.
If you're in this market, you might also want to look at HAG Capisco Chair: I Measured the Sit, the Tilt, and Where the Money if you're considering a pricier option. But for budget chairs, the same rules apply.
I can't tell you which chair is the best because we're built differently. But I can tell you this: measure your thigh first. That's the mistake I made every time until I didn't.