The job of the rockets isn't to gain height (that is a side effect), unless you are working with a sub-orbital design. The job is to accelerate the payload to around Mach 25 or so. The reason this is challenging is that you not only have to accelerate the payload, you also have to accelerate the fuel, fuel tanks, engines, and other associated hardware too. Which is why the promising techs mostly revolve around using less fuel (such as rail launch for the initial oomph), or something like scram jet for the first stage (they part of the fuel and reaction mass comes from the atmosphere for the first few Mach). Or something that has very small fuel amounts, and only caries reaction mass (nuclear with H2O as the reaction mass).