Two-line atomic fluorescence (TLAF) thermometry is based on the consecutive excitation of two nearby atomic ground states to a common excited state, and ratioing the ensuing fluorescence yields. TLAF is one of the few methods that hold promise for thermometry in sooting environments. We extend the method to the regime of fully saturated excitation and introduce a new seeding system that also allows the method to be used in lean flames. We compare results for saturated TLAF to those of linear TLAF and to thermocouple measurements, and find good correspondence. The saturated version introduced here maximizes fluorescence yields while simultaneously suppressing the dependence on excitation laser irradiance.