Random thoughts:

(a) are you anywhere near a Design Within Reach store? Owned by Herman Miller, this is where you can sit in their chairs including the Aeron. The Aeron mesh has plenty of give to it for comfort: for me the disadvantage of the mesh seat (any mesh seat) is the hard plastic frame around it, if you are someone who moves around on the seat a lot or likes to bring up one or more legs the frame can be uncomfortable.

(b) you can get decent inexpensive chairs on Amazon. The Clatina Mellet for one gets frequent mention as a good cheap chair with a zillion adjustments so you are likely to find it comfortable. Biggest difference from the top brands is that you can't expect it to be as durable.

(c) my chair is worth considering for you: a Haworth Soji. I'm 5'8 160 so probably a bit taller in my torso than you and I'm sitting with my back firmly against the backrest up to my shoulder blades. Haworth is not as commonly recognized as a top brand as Herman Miller and Steelcase but they are quality chairs with a long warranty. The best deal price-wise if you are interested is the "Quick Ship" in black or black/grey. This has all of the adjustment options except for the "forward tilt" which you would never use. The Soji is at the bottom of the range of Haworth chairs, this is a decent video quickly reviewing them all.

(d) finally: top tier chairs tend to have firm seats because this promotes ergonomic sitting - that's the theory anyway. The Soji might be firm for you or you might adapt after a few days, hard to tell - Haworth does have a 30 day return. The Leap V2 you've had recommended to you is notorious for the firmness of the seat - people who otherwise love the chair design and have the money have been known to buy a Steelcase Amia solely to swap the Amia seat for the Leap seat, apparently they are compatible.

The Clatina Mellet is considered a decent "cheap Amazon chair", noteworthy that they offer a 5-year warranty which is long by category standards. There's also versions without the headrest for less $ I think.