Flat leather with no indented or raised pattern is HOT. Probably will buy some sort of cloth seat cover in an attempt to avoid this. If you live in a cold climate, you could just turn down your heater and it wouldn't be an issue. Also causes back to be hot, but using lumbar support cushion, removes the problem. As for the other issues of the chair, the seat is a bit softer towards the front and a bit firmer towards the back, so using the lumbar pillow pushes you forward some making the chair more comfortable.
As I stated before, the lumbar pillow on these things are not comfortable, though. I've isolated the problem being due to the edges on the side of the memory foam pillow curving outwards which causes them to poke into your kidneys. So as you can see, 99% of the issues with this chair revolve entirely around the lumbar cushion. I will probably attempt to perform surgery on the foam to make it flat instead of curving outwards to fix these issues. It's difficult to see in the picture, but those raised edges on the sides stick right into your kidneys:
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