I'm late seeing this but I'll give you my best argument for physicalism (or first attempt). We start from our mental worlds because that's the mode of our brain function. So for me the idea that the physical world is primary is an assumption, not a proven fact at least not on the first attempt. Also, if you assume the world is physical and everything is based on physical matter then you do have the problem of how do 'non-physicals' exist. For me that is the logic problem at the heart of philosophy. Is it monism or dualism?
Well, we shouldn't just take a guess, so where to start? Okay, assuming physical matter really exists then non-physicals should definitely not exist. Non-physicals are by definition non-existent. That's logical right? But we deal with non-physicals all the time in our mental worlds.
Zero, the past, the future, numbers, theories, ideas, words ....and once you see the pattern in all the easy things you can arrive at the conclusion that all mental content is non-physical. But the thing is it's based on physical brain state. A brain is always present, in physical location and physical time, when this perception of non-physicals is occuring so that is the basis of claiming (the ability to deal with non-physicals is a special ability of our biological brains). The logic is we see the components coming together in a physical way that makes the non-physical a tenable proposition. As opposed to a logical impossibility a paragraph ago.
So back to the argument of does physical matter exist. Now you have the logical conclusion that physical matter must exist because the mental worlds we experience could not exist without a physical basis.
So to call it monism or dualism is a linguistics problem that should be postponed until you understand these relations.
I would say all is physically based but our brains have this ability to deal in the non-physical realm.
There is an extremely good application of this principal in the field psychology and psychiatry in solving psychosis and schizophrenia (not endorsing the terminology, it's archaic). The assumption has been these condition are biologically based (strict physicalism) but the evidence points strongly to non-physical mental content driving these unfortunate conditions which are then treated with forced medication.
Or here in Minnesota, forced enrollment in clinical drug trials for the pharma industry leading to the suicide of the patient. No small matter but nowhere near the end of the problems of getting it wrong.