We minimally extend the Standard Model (SM) with a ${\mathrm{Z}}_{2}$ symmetric potential containing a single scalar field, serving as our inflaton with a quartic self-coupling. In the model we have symmetry breaking in both sectors, and with the addition of an inflaton-Higgs portal, the universe is able to efficiently reheat via 2-2 inflaton-Higgs scattering. Assuming that the universe with a positive cosmological constant should be metastable, only one particular symmetry breaking pattern in the vacuum is possible, without the need to finely tune the Higgs quartic self-coupling. Inflatons with masses in the range $O({10}^{\ensuremath{-}3})\ensuremath{\le}{m}_{\ensuremath{\chi}}\ensuremath{\le}{m}_{h}$ and mixing angles that span ${\ensuremath{\theta}}_{m}^{2}=O({10}^{\ensuremath{-}11}--{10}^{\ensuremath{-}2})$ evade all current cosmological, experimental, and stability constraints required for a metastable electroweak vacuum. Upgraded particle physics experiments may be able to probe the parameter space with ${\ensuremath{\theta}}_{m}^{2}\ensuremath{\ge}O({10}^{\ensuremath{-}4})$, where we would observe trilinear Higgs couplings suppressed by up to 2% compared to the SM value. However, to access the parameter space of very weakly coupled inflatons, we rely on the proposals to build experiments that target the hidden sector.