Portable oxygen tanks are not practical unless you are on a Himalayan expedition above 20,000 feet, or unless you have a serious chronic disease.
For your first trip to high elevation, you really need to be a little cautious. After that is successful, you can push it a little more each time. I know people at both extremes. One guy (geophysicist) knows that he will get a splitting headache as soon as he has been above 11,000 feet for an hour. It gets him every time no matter what he does. Some of us have a more normal response. That is, the first time up it will slow you down tremendously, and you may need aspirin for headache. Little by little, time after time, your body learns how to respond to that, and you will learn to drink more water. You can learn what your own body requires.
The old axiom for expeditions is to keep pushing your camps up higher and higher daily, but not to try to gain a net of more than 1000 vertical feet per day. My personal opinion is that the axiom is overly conservative, but it is OK if you don't know any better.
My personal opinion is that 80% of the high altitude symptoms that people have can be traced back to simple dehydration. So, maybe drink more water and add in a bit of Gatorade. The other thing is that it helps to be somewhat in shape. You don't need to be an Olympic marathoner, but your legs have to be ready for a workout.
Every year I hike up Mount Whitney. I can almost guarantee you that if I simply drive up to the 8000 foot trailhead and start, the altitude will catch up to me before I am halfway up the trail. Instead, I go "hang out" at some high car campground (maybe 8000-9000 feet) for a few days, and I take dayhikes up from there. That gets my body more tuned in to what it needs to do. Basically, my respiration gets deeper but not much faster, and my rest heart rate increases slightly. Once I see that my own body is functioning normally, then I head to the Whitney trailhead and start.
If you want to make a guess about your own high altitude ceiling, then try this. At sea level, record your rest heart rate and your maximal heart rate. Now go up to 5000 feet, for example, and repeat those recordings. Now go up to 10,000 feet, for example, and repeat those recordings again. What normally happens is that your rest heart rate keeps increasing as you go higher, and your maximal heart rate keeps decreasing as you go higher. Plot that out on graph paper, and you will see that the two lines will converge at some point. It may be 11,000 feet, or it may be 16,000, or something else. That is your ceiling, and you are unlikely to make it far beyond that. If you hang out at high altitude for a week or more, your body will begin an adaptation process that involves blood chemistry. Then the two lines will begin to shift a little, and you may get a better ceiling.