I don't think there a lot of things more difficult to make than a chair, and what's a barstool (that has a seat back anyway) other than a tall chair? They need to be comfortable first and foremost, nice to look at, and both sturdy and safe. This is a build video of the first time I've ever attempted to make something quite like this. I mentioned that I'd provide links to the hardware that I used, so here it is:

On the stool:
Upholstery Fabric: https://www.amazon.com/dp/B084P8C3BK?...
Foot Rail Cover: https://www.amazon.com/dp/B08RQPRT5D?...
Swivel Mechanism: https://www.amazon.com/dp/B00GYJW40U?...

In the cushion:
Batting: https://www.amazon.com/dp/B08R69GKL1?...
Nylon Webbing: https://www.amazon.com/dp/B08BNNKV9M?...
Foam cutter: https://www.amazon.com/gp/product/B07...
Upholstery Foam: https://www.amazon.com/dp/B00TSVSA7C?...
Upholstery Batting: https://www.amazon.com/gp/product/B01...