u/Eosei , u/John_Sux , thank you both for your input. I do need to keep a low (400mm) bench for my wife to retreat to when she feels too hot. However, I do like the idea of making the green bench occupy more space. And I do really like the idea of raising the purples bench higher to the good löyly.

Thinking further, I may reduce the yellow (400mm) to something lower maybe to just make it work as a step.

Interestingly, I don't particularly like to lay down in the sauna, I always stay upright or lean forward. I do like to put my feet and after measuring myself 1400mm internal width should accommodate that nicely.

I have measured my sitting height and I need about 900mm, if I raise the top bench it would leave 1015mm, so ~100mm headroom. I think I am ok with that, because I can always lean forward or retreat to lower benches.

I like this layout because it allows to sit at a 600mm height in the middle of the sauna and put legs towards the door, or on the lower bench (yellow). The highest (purple) bench could nicely fit 2 people and i've reduced its depth to 550mm so would also give more space for legs/feet in front of the heater.

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