We present our current results from ongoing lattice investigations of the Berenstein--Maldacena--Nastase deformation of maximally supersymmetric Yang--Mills quantum mechanics. We focus on the thermal phase structure of this theory, which depends on both the temperature $T$ and the deformation parameter $\mu$, through the dimensionless ratios $T / \mu$ and $g = \lambda / \mu^3$ with $\lambda$ the 't~Hooft coupling. We determine the critical $T / \mu$ of the confinement transition for couplings $g$ that span three orders of magnitude, to connect weak-coupling perturbative calculations and large-$N$ dual supergravity predictions in the strong-coupling limit. Analyzing multiple lattice sizes up to $N_{\tau} = 24$ and numbers of colors up to $N = 16$ allows initial checks of the large-$N$ continuum limit.