As known because of the rarefied air, the blood in the mountainous regions is less saturated with oxygen. Because of this, the inhabitants of the lowlands who got there often feel weakness, malaise and other symptoms of altitude sickness, up to a change in consciousness.
Sherpas, a people living in the east of Nepal, in the vicinity of Everest, face these difficulties much less. They are perfectly adapted to the conditions of high mountains, they are hardy and therefore often serve as guides and assistants to climbers climbing Everest. In addition to endurance, Sherpas enjoy several other bonuses to the mountain habit, such as high reproductive success. This means that Sherpa women are more likely to successfully become pregnant and give birth to live children more often than representatives of other nations in the same conditions.
Sherpas are helped to adapt to the highlands, in particular, their blood. Highlanders generally produce more red blood cells (about 1.5 times) than lowland dwellers, which allows them to carry more oxygen, while Sherpas synthesize even more plasma, making their blood less viscous, which means that they can move faster through the vessels and thereby carry oxygen faster, as a result of which the load on the heart decreases.
However, starting from an altitude of 8000 meters (or any other altitude at which the atmospheric pressure is below 35.6 kPa (267 mm Hg), the oxygen level in the air is insufficient to support human life due to prolonged stay at such an altitude a person will need an oxygen balance.
And here we come to the essence of my question: how should the respiratory system of my genetically modified people be arranged so that they have the opportunity for a sufficiently long time without any health risks with a similar lack of oxygen in the air?