My guess is that if the oil change and oil pressure sender happened at the same time and you still had a low oil pressure problem, you likely have significant bearing wear that will only be temporarily patched with heavy oil, assuming you can get the sludge blobs out.
Bearing wear test:
I should run a simple oil pressure test, and if at idle I get lower than 10 psi then....maybe I’m screwed..?
What is the commonly accepted min oil pressure figure at an idle of, say, 1,000 rpm..?