There just isn't any way to get by with one knife. If nothing else you need a small knife and a big knife. There is some degree of latitude with a big knife and a small knife, but a medium sized knife will just not be suitable for too many things at either end of the range.
After I left home and got my first apartment I did well enough with just two knifes, and yep you guessed it, a big one and a little one. Today I'm like most cooking enthusiasts with a big, fully stuffed knife block set and other knives (including a cleaver) that I use less often kept in a drawer because don't need them at hand. (Particularly that cleaver! It would really be nasty to drop it and have it land on your foot!)
Here is what I would recommend if you could have just two knives: 4" paring knife and a 6" chef knife. Or you could go with maybe a 5" serrated utility knife and a 7"-8" chef knife. Or even a Santoku instead of the chef knife.
Most chefs probably would criticize my 4" paring knife and go with the 5" utility knife but I've got both and I use the paring knife far more often than the utility knife.
One good thing, in real life you can have as many knives as you want!
Even too many, although I'm not there yet. (Yeah, right.)