I sweeten most of the time. Usually with a brown sugar cube, unless I’m out, and then usually Demerara sugar. Small amount, like half a teaspoon. Sometimes I do a drizzle of maple syrup, and holy hell is that yummy.
To be fair I did this mostly when I was bartending and had lemons for garnishes in spades. But you can do it at home as well. Just use a carrot or potato peeler, take your lemon and peel off a slice and twist the lemon peel over the espresso. You will see all of the oils in the rind spray into the liquid. Then rub the rind over the rim of your cup. As for the lemon, it's still good. If you keep it in the refrigerator it will be good for days. Keep using the rind for your drinks, and then cut it up and use the lemon for lemon water, or cleaning your microwave, or tea, or whatever. Lemons are cheap and versatile.