While it is not conclusive it is very likely that the initial amount of virus you get infected with will go a long way to determine the severity of your symptoms. After infection, there is a race between your immune response and the virus's ability to replicate. If the immune response wins early, you will have only minor symptoms or perhaps even none at all. So while a surgical or homemade mask may not prevent infections, having a simple physical barrier will likely reduce the number of viruses that get to you and therefore the severity of the disease.
https://www.nytimes.com/2020/04/01/opinion/coronavirus-viral...
Get an oximeter. This device measures oxygen levels in the blood. It is believed that one reason covid19 kills is that it can cause low oxygen levels (hypoxia) without severe symptoms. This means that people get to the hospital too late. If you do get sick, an oximeter is useful to have (though they are hard to get now for obvious reasons). Make sure what you get is FDA approved.
https://www.nytimes.com/2020/04/20/opinion/coronavirus-testi...
