At the risk of blowing my own trumpet (but, hell, I am proud of it), my highest point is the summit of Mera Peak in the Himalaya at 6476 metres (21,247 ft). I now live at about 40m asl.
[Rosie] No, my fault, not yours. I just remembered because my highest is almost identical to yours, but in a completely different part of the world (Colorado Rockies).
[Rosie] - No oxygen. I was slowed down by the lack of it, but not reduced to gasping. The main effect was that I lost my appetite completely. I was there in March-April, so pre-monsoon. Overnight it was regularly down to about -20°C. During the day there was a lot of bright sunshine, but I reckon the shade temperature didn't get above freezing; it was fleece jacket, thick gloves & balaclava even when working quite hard and down clothing as soon as the sun set. Mera is the highest 'trekking peak' in the Himalaya, anything over 6500m is a 'climbing peak' even if there is no technical difficulty. However Aconcagua is higher and presents no technical difficulties and is only about 20km from a good motor road. It's probably the ultimate challenge for the non-climber.