Honestly, you’re probably better off just buying a reusable half-face respirator: https://www.grainger.com/product/MILLER-ELECTRIC-Half-Mask-Respirator-Kit-36RC58
They’re more comfortable that you’d expect, offer vastly superior protection, and are far more convenient than having to fiddle with different reusable masks as they fall apart. It’s also probably cheaper than constantly buying new reusable masks. The linked mask is $43.27 and (depending on location), should arrive in a few days.
Those are fine. I would give them a 3/10 for comfort, 11/10 for efficacy, and 3/10 for price, since only the respirator part is reusable and you have to buy filters. A good choice if you in a very at risk demographic and don't mind spending the extra money.
For comparison, I'd give the modified KN95 a 6.5/10 for comfort, 7/10 for efficacy, and 8/10 for price.
Looking at amazon, kn95s cost ~$1 per mask. Replacement filters for the mask I listed cost $18 for the pair. If the mask filters last > 18 times longer than the KN95, the mask is cheaper.
There are two types of filters. Gas filters inactivate harmful gasses with chemicals in the filters. They need to be changed often because the filter runs out of chemicals. Particulate filters remove particulates from the air. They need to be changed once the filter clogs up with particulates. If you’re not using it to filter smoke/dust/ect, they can last a long time. I’d change at least once every 6 months, but that’s $36 per year in mask costs, which is pretty small.
As someone who exclusively uses respirators, I’d say they’re actually reasonably comfortable once you get used to them.
If you have a disposable n95 that's been worn past its usefulness, you can cut out the metal nose strip from it before discarding the filter instead of buying nose strips separately.
Back when there were no masks to be found and cloth masks had to be made at home, I found that the green soft-plastic-encased floral wire from the dollar store had the perfect stiffness and softness to make mask nose bridges. (The darker green wires without the soft plastic, sold as vegetable ties, were not stiff enough to secure the masks well when I tested other options)
If tightening the ear loops enough for a good seal makes them hurt your ears, you can transform any ear loop mask into a head band one. You can use 2 buttons and some elastic, or cut a piece of soft but not too flexible plastic to shape, or 3d print the device that makes this conversion. It's called an "ear saver"; an image search of that term will show lots of options.
Like the idea of ear savers; might try them to see how they feel compared to the tight earloops.
There have already been a couple of posts on this topic, including this one which promotes a mask brace:
https://www.lesswrong.com/posts/CrikcGiaWK9CSSzrJ/i-made-an-n95-level-mask-at-home-and-you-can-too
Since then, there have been changes to the way we mask. Nowadays, I often see people wearing KN95 masks outside, whereas in April/May almost everyone stuck to plain surgical masks. In my opinion, KN95 masks are a great compromise between surgical and N95 cup or duckbill style masks; they offer pretty good comfort, good filtration, but unfortunately most of them do not offer good fit.
One of the reasons for this is that KN95 masks are more commonly found in earloop form rather than headband. I haven't tried the headband KN95 masks myself, but the earloop masks fit loosely around the ears and don't seal the outer rims of the mask to your face. Another major reason for leakage in KN95 masks is that the bendy bit around the nosebridge isn't really firm enough, and so these masks, (at least when I use them straight out of the box), leak a bunch of air through the top. This is most noticeable if you wear glasses or goggles; they start fogging up.
The main solution that people use for the glass fogging issue is tape around the top of the mask. I dislike this approach for a few reasons. First of all, tape on your face feels bad. Secondly, every time I tape the top of the mask to my face, the tape loses stickiness and I have to tear it off to replace it with new tape. This visibly damages my masks, which I reuse at least several times.
Here are some of the ways I modify my KN95 masks to maximize comfort, fit, and reusability. You will need:
Other than the metal strips, you probably have all of these lying around already! Here's a self explanatory picture with additional explanation below:
A few things to notice. First of all, the earloops have been tied and then snipped to be smaller. This makes the mask fit tightly around your face. You may have to experiment with how much you want to tighten it, since not all faces are the same size. Once you have tied the knots, just take your scissors and snip off the dangly loops.
An additional metal strip was added to the upper part of the front of the mask. Make sure to bend this to the shape of your nose.
I've also folded up a wad of toilet/tissue paper about 1-2mm and glued it to the inside of the mask. When I showed this part to others they usually think it's dumber than the rest of the adjustments. But believe me when I say this really helps with eliminating the glasses fogging and air leakage through the top, at least for my face shape.
There you have it; easy ways to make your cheap KN95 masks really good at actually filtering the air instead of just having you breathe around the cloth.