Unfortunately, there isn't a good altrenative for you. I think the self fill is probably the best there is unless you can learn to carry more weight.

Hello Mae. There are NO portable units I have seen that offer CONT flow. Even IF they did, the battery life would be poor to say the least. Instead of toting tanks around, you would still have to have a bag full of batteries to go far away from home.
While the E-sized tank (about 3 feet tall) seems heavy, it is best used with a rolling cart. A full tank holds 660 litres of O2. At a 2L/min flow rate, that's over 300 minutes (about 5 HOURS) of AIR supply. Besides a good movie theater, there at not many places I want to go that will take that long anyway. 🤔

I have links on my Profile story covering all the ratings of the latest Portable brands. But the Tanks have proven the best for me all the way around. They may seem clumsy, but the make ROOM for me at places like Walmart and CVS. 🛒🏎️ Of course, your mileage may vary.
be Well

I don't walk ; like I use to, I am using a wheelchair when I go out! Don't like my iongen I use the cylinders a to also!