What is our current understanding between the ratio of Earth's interior heat between the downward pressure and atomic decay?
There is no heat caused by pressure. Heat increases with depth, like pressure, so the two show a correlation, but this does not imply causality.
The two main sources of Earth's internal heat are radiogenic heat (as you said) and primordial heat, that is the kinetic energy turned into thermal energy during the accretion of the planet. There are also minor sources, like tidal heat caused by the Moon, and latent heat caused by crystallization of the liquid core.
The total heat budget of the Earth is pretty well constrained: we can just measure the heat flow coming out at the surface (in W/m$^2$) and multiply this by the Earth's area. The current estimate is ~47 TW (Davies & Davies, 2010). Getting ratios between sources, however, is more difficult, and rely mostly on modelling. See for instance the work of Dye (2012), who proposed a radiogenic heating of 15–41 TW, while other authors (referenced by Dye) proposed 12–30 TW of primordial ("fossil") heat. As you can see, the uncertainty is still quite high...