Tl;DR: I don't think that a radiative planetary atmosphere is possible. It seems unlikely to meet the key requirements of surface gravity, opacity and temperature that would ensure that radiation would dominate over convection.
We can answer the question of whether radiation or convection dominates energy transport by taking a cue from stellar astrophysics. Many stars form separate radiative and convective zones, while others are fully convective (e.g. very low-mass stars) or fully radiative. For example, the Sun's core is surrounded by a radiative zone that extends about two thirds of the way to the surface; beyond that, convection transports energy the remaining distance to the photosphere. We even see differences in stellar atmospheres; in the atmospheres of hot stars, radiative transport is more important, while in the atmospheres of cool stars, convection is more important.
Let's start by trying to determine whether convection is possible under a given set of conditions. There are a couple of ways we can write the convection criterion. It's often presented in terms of density $\rho$ and pressure $P$:
$$\left|\frac{d\ln P}{d\ln\rho}\right|_{\text{ad}}>\gamma$$
where $\gamma$ is the adiabatic index and $_\text{ad}$ indicates that we're talking about an adiabatic gradient. However, we can also invoke the ideal gas law and think about temperature, rather than density:
$$\left|\frac{d\ln P}{d\ln T}\right|_{\text{ad}}<\frac{\gamma}{\gamma-1}$$
The left-hand side is often denoted by $\nabla_{\text{ad}}$. We reach the boundary point when the radiative and convective gradients are equal, $\nabla_{\text{ad}}=\nabla_\text{rad}$, and we have a nice expression for the radiative case:
$$\nabla_{\text{rad}}=\frac{3F\bar{\kappa}P}{16\sigma T^4g}\propto\frac{\kappa}{g}$$
where $\kappa$ is opacity and $g$ is acceleration due to gravity.
In short, we need a large radiative gradient $\nabla_{\text{rad}}$ for convection to dominate over radiative transport. This occurs in regions of high opacity or low gravitation acceleration; in regions of low opacity or high gravitational acceleration, radiative transport dominates. For radiation to dominate, we need the reverse: we want a planet with a low-opacity atmosphere and strong surface gravity. The surface gravity can be addressed by making our planet small and dense, made of a mixture of iron and silicates, but this may not be enough, and so we still have to consider opacity.
Planetary atmospheres contain sources of both continuum opacities, such as aerosols and water droplets, and line opacities, such as molecules that can undergo vibrational and rotational transitions (Fortney 2018; see also these notes). Line opacities tend to dominate, and so we could argue that we could reduce atmospheric opacity by simply removing some of the most common absorbers: water, methane, carbon dioxide, carbon monoxide, ammonia, etc. For an atmosphere of near-habitable temperatures, water, methane and ammonia are key in the optical and infrared range - perhaps a dry atmosphere could reduce key water vapor absorption bands.
Unfortunately, there's still one problem: $\nabla_{\text{rad}}$ has a very strong ($T^{-4}$) temperature dependence. Terrestrial planets tend to be quite cool compared to stars, and so we should expect a strong decrease in the radiative gradient from that alone. While it's true that some hot Jupiters may rival stellar atmospheres in temperature, they can't reach the temperatures of the hot, massive stars for which radiation dominates over convection in their atmospheres.
Even without any numbers, I'm inclined to say that it's not possible for you to completely get rid of convection. Sure, you could severely reduce line opacity, but that would require a dry atmosphere, which seems unlikely if you want oceans. You'd also need a high temperature, and even if that was attainable, it would lead to increased evaporation from said oceans, and more water in the atmosphere, and thus a higher opacity. In short, I don't think you're really likely to have a planetary atmosphere without convection.
