I'll try to keep this short - which is not my strong suit! I apologize for threadjacking, in advance.
I considered chairs with backs. I didn't find one that I liked. Many that are padded have overly soft centers and a frame around the edge. Sitting forward isn't comfortable. Some slope to keep you in the seat. Others are too hard or the wrong height.
I was interested in the "Nota Music Posture Chair", online, but I never found an example to try out locally. It looks like a good design but it has a metal frame and would have been more difficult to modify than wood, if necessary.
When we got our piano, I really liked the bench. Here's a picture:
The padding is dense and my bones don't contact the wood, unlike my previous cheapo folding keyboard bench.
Our piano bench goes low enough for my legs to sit level. I need it all the way down. Unfortunately, my daughter needs it up at the height pictured for playing piano. I need it in my office for practicing guitar. My daughter needs it in the living room for practicing piano.
War ensued. I lost.
I hunted around to find something similar and found "Adjustable Pillow Top Genuine Leather Artist Piano Bench in Walnut Satin" on Amazon. This is the kind I bought.
Here it is in my office:
It meets my needs for a supportive dense pad that spares my bones from pressure. However, it sat higher than I thought ideal. The legs are attached with hex key bolts. I removed them, unscrewed the cheap little feet and trimmed about 3/4" off the wood from the ends on my table saw. Then I added felt pads:
I'm enjoying the result. I really do need a nice level thigh for using my guitar support and this meets that need. Between the effective padding and the guitar support, I can go as long as I want to and I'm not limited by my back. Now, I just have to deal with shoulders and elbows!
"If I have seen further it is by standing on the shoulders of giants." -Sir Isaac Newton
Armin Hanika 56PF