BTW, my grandmother made the best coffee all of her life by boiling the grounds in an enamel saucepan (stained an ugly color by the end of her days) and straining it into the cups. She called it “hobo” coffee. Sometimes she put eggshells in it.
LOL! My grandfather did the exact same thing, including the eggshells. I did not drink coffee at the time, but my father did and would not touch what my grandfather made.
Then I use a stainless steel saucepan, small, heat the water to boiling, turn off, put the ground coffee in it and let it steep for a few minutes. Then pour through a small sieve (I have a cheapo plastic one with a fine mesh).
My mother used the egg shells sometimes. She said water is a key component. She would know certain places where the water made better coffee. So maybe bottled water?
You have to experiment.
And if you don't have a grinder, you can put in a plastic freezer bag (baggies too thin) and pound with a hammer.
Right now I have some nice dark roast Starbuck's beans and keep them in the freezer.