DIY

I don't know if they're still selling them, but I have masks from Outdoor Research which have removable, replaceable filters. They are not (K)N95 rated, however.

Edit: I should have just looked it up really quickly. They are still available if you're interested in trying those. It looks like they're going to stop producing/selling them soon.

https://www.outdoorresearch.com/collections/face-masks-and-filters

So have you looked at using a N95 filter in a respirator?

I don't know if that'll work for you, but they certainly stay in place much better than any mask, and there's a wide variety of them that have the filter in various locations so maybe that'd be a better option?

You look a little bit Fallout while wearing them, but they're super comfortable for hours (because that's how people who wear them use them), cheap to replace the filter when the time comes, and they seal spectacularly well and are easy to fit.

This is the moment where a kind product designer should step up and design you a Mad Max type of mask. People are watching you so you'd better give them something to watch ;-) Sorry, no advice about existing masks. Good luck!

Hmm, difficult question. I think in the end the most important part for your own safety is a tight fit of the mask, and that is hard to do with cloth masks in general.

Detachable filters usually require a more full rubber face piece with large straps to hold it in place. Such a mask could maybe be modified to have some chin nub or so that fits well to your wheelchair control, but I am somewhat doubtful that will be comfortable.