Try a few(!, as in, 3-5 single grains) of salt to reduce acidity. For body you could try French press or mesh filtered, gets more chewy mouthfeel but that's a coin flip if you might like it or not.

Have you tried doing your own cold brew concentrate and then cutting it with water and Ice before? It really changes the profile of some coffee.

There is also the phrase garbage in garbage out, so if your starting with a low quality bean or over roasted bean you could be missing out on all the natural flavors in coffee.

Im lazy so I generally just do a simple Chemex filtered drip but even that created a cup miles better than any kurig or mr coffee equivalent that I found out I could really enjoy coffee without adding anything.

If I end up at Tim's or Dunkin then its a shot of mocha because I struggle to drink their coffee black because of how over roasted the beans are. They cook all the flavors out of it to make it "consistent."