If you wanted a completely surface world, you can generate a world with no underground layers whatsoever.
If you set the cavern layer count to 0 and turn off both the bottom layers it completely removes the underground. Then you can up the levels above ground a bit to give you room to build towers and the like if you want more than the default 15. Doing this you can get a world with nothing but the dirt level (1 level underground, would let you dig channels on surface layer but no deeper) and the surface, as well as any sky levels. No rock whatsoever unless you embark on a mountainous area.
The upside is you can get really good framerate with so few z-levels. The downside is that you never get to fight the underground critters, but you could still fight goblins and wandering megabeasts. Or you could set cavern layer to 1 and just have a very small underground, then try to find a cave with an entrance to it - that way you could still have underground invasions and somewhere to explore without actually mining.
It might be interesting modding the game to allow you to play humans, then building yourself a human village and settling by a river for water. With so few z-levels you could probably get a really good framerate going even with a big population.