At what altitude can I travel in 27w ??

What is safest high altitude to travel during 27 to 28 w ??

Can I travel via plane to 8,000 meters altitude above sea level ?

My residency is on sea level .. does the heigh altitude also effect the oxygen breathing level ? I wana travel and change my mood but quite worried that would it be safe for my baby ? Going to high mountainous region will b fun with fresh air but won’t it be trouble ??

Kindly suggest … I am gonna b first time mom at 35 years ; I don’t have any medical issue ..