Here's some things to consider. Any particle under 1 micron is the most damaging, these particles can (and do) travel all the way to your Alveoli (the pockets inside your lungs where the actual oxygen/CO2 exchange happens) Once a particle is inside your alveoli, it will be there forever, the cilia in your lungs cannot clean your alveoli. So getting these particles are the most important.
There are lots of options available for respirators/dust masks. The most important thing about the respirator is that you ACTUALLY USE IT. No matter how good the filtering, if it's uncomfortable or a PITA to use, then you are less likely to be wearing it.
I started out with the half face respirators and wore them under my face shield, but only when I had to. Recently I aquired a PAPR (Powered Air Purifying Respirator) Now I wear it ALL the time! I personally opted for a 3M Adflo system (not a cheap investment by any means) but it protects my lungs and my face, my glasses don't get sawdust all over them, and I can breathe when I'm done.
“I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.” ~ Albert Einstein