You definitely get what you pay for with office chairs. Moreso the ergonomic variety and not the terrible race-car-seat "gaming chairs".

Honestly, if you're paying less than $500 for a chair, be prepared to buy another one in two years or less if you actually plan to put in many hours on it, especialy at your weight. Cheap chairs start to break down quickly, with their immediately-flattened foam, particle board components, and cheap fabrics. None of it holds up well to pressure or long-term use. Think of the investment in terms of how long you'll use it: if you spend $500 and don't have to replace it for 10+ years, $50 per year is a pretty reasonable price to pay. I know the upfront cost is high, but it makes a huge difference in the quality and lifespan of the chair.

I just bought a chair myself a few days ago that will take most of a month to be constructed and get here, but my $700 Ergohuman chair has had another major failure for the second time in 10 years, so I figured it was time to buy something hopefully even more reliable.

I had to do a lot of research to find something that suits my height (the lumbar on about every chair I've ever seen seems to hit me in the tail bone instead of the lower back and I'm only about 6'1" - or 185 cm to you) and it's getting harder to find good ergonomic chairs with headrests. I ultimately decided to pay a fuckton for a Steelcase chair, as I hate mesh, hate Herman Miller, and I basically spend a third of my life in it. Skimping would be like buying a bad mattress and expecting to feel good after sleeping.

Anyway, I'd look over recommendations from sites or perhaps YouTube channels that review office chairs regularly. Use that to browse around and see what you can find at a cheap price from an online store that might be getting rid of some things that would work for you. (If I hadn't wanted a chair with a headrest, I probably could have gotten the same model on sale from one store for about half the price I paid.)

If you're sedentary and have weight issues (as most of us start to as we age), you definitely have to look out for your back as best you can, in all your furniture. Soon enough, you'll find your back getting tweaked just from laying wrong on the couch or in your bed.