First off I'm really sorry you're in the situation you're in, having a public facing job makes this so complicated. I don't have a perfect answer and these things may or may not work depending on the details and context of your job, and also what you can afford.
All of these suggestions are based around the principle of harm reduction, no single one of these interventions is going to reduce risk to zero, but that is never the point nor is it entirely possible yet. Combining multiple of these suggestions can reduce risk even further than just doing one of them.
1) If it's possible to convince your employer to let you bring a HEPA grade air purifier to set up next to you while you work (as I assume it's indoors) that can be helpful at reducing risk. Depending on the size of the room you're in will determine what size of purifier you want. Some arguments that are not about illness that can help convince an employer include a) reducing allergens b) improving cognitive capacity -> improved work output (a study)
2) Test on a weekly basis with rapid antigen test - again not a perfect solution, rapid tests have a high false negative rate (~66%) and are more Accurate when taken multiple times in a row, but this is again better than nothing and testing multiple times a week could become very expensive.
How to make rapid testing more affordable? I do a regular group buy with friends of these 4-in-1 rapid antigen tests (COVID/flu a/ flu b/rsv) from Altruans website and they come from Europe and the shipping / tariffs are expensive if you only buy 5, but if you say buy 150 like I did with my friends, the cost came down to $2.13 per single box test (including the shipping/tariffs per box.) If you have friends who would get in on this, you can make rapid testing once or twice a week very affordable for you.
A NOTE ON MAKING RAPID TESTING MORE ACCURATE; a recent study was published suggesting that many rapid tests brands have better accuracy when you wait to check the test at the end of the interpretation window. Typically a test will instruct you to view the results only at the start of the interpretation window (which is x minutes after you add the liquid drops to the card.) The end of the window is indicated where the instructions say "test results not valid after x minutes." Checking closer to this end of the window in the study caught a few more positive results that had been negative at the start of the window. So factor this into the time you set aside for rapid testing!
3) you didn't really ask this but in case it could be helpful, there could be ways to make mask wearing more tolerable. One is a desk fan pointed to your face, it can make a huge difference!! If you can't have a desk fan because you move around a lot, they also sell shirt fans that clip to your belt loop and blast air up inside your shirt, which I think theoretically could also hit the underside of your mask and help your face cool off. They also sell neck fans that look kind of like headphones but you wear it around the back of your neck and it blasts air directly to your face, but it depends if your boss would let you wear something that resembles headphones.
Another is finding the right mask for your face that maximizes breathability - depending on your tolerance this may or may not work but I believe is worth trying to find out, as masks still remain far more effective than the first two options!
Personally, I find the BNX black duckbill N95s to be the most breathable to me (I find they are only available on Amazon at least where I live). I live in TX, it gets HOT AF and I can wear this outside, I still sweat, but it's not nearly as bad as a 3M aura or other more structured respirators.
Some people really swear by the 3m Vflex, personally it doesn't fit my "ethnic" facial features well, but if you don't have a super pronounced nose it could be a good fit.
You can buy a sampler pack of a ton of different N95 masks here to try, note they do not include the BNX ones I recommended but do include the Vflex. I don't know if you live near a mask bloc but if you do, definitely check them out as a resource as well.
Also worth noting that sometimes (not always depending on your illness) you can build tolerance to masking by building a regimen, starting slow, taking breaks, like you would do for exercise. Some people who mask at the gym use masking as an endurance check! I also in the summer like to work on my heat tolerance by taking a walk at night, and then slowly going earlier and earlier, while also taking breaks, using cooling strategies, etc. And eventually introduce masking into the equation to better help my tolerance with masking in the hot outdoors. It may be worth trying to do this outside of work until you get to a tolerance where you can do it at work, and remember it's ok to go slow and take breaks, even at work!
If you end up trying some other masks / trying to build endurance and they don't work for you, that is Ok, you made a valiant effort to find something that works for you. Not everyone is able to mask in all situations. That's where points 1&2 can be helpful, because even if they're not as effective as masking, when it comes to COVID, doing /something/ is better than doing nothing.
And lastly, please check out this other post where I added information on what to do if you get COVID, because the best preparations include contingencies for worst possible scenarios.
