The surface layer is mostly irrelevant for life conditions when considering oceans enclosed in ice. Even a few meters under a water ice surface you already have plenty insulation from surface temperatures, whatever exothermic process you get going is going to stay warm for a long while.

Europa surface is actually more hostile for life due to the heavy radiation from Jupiter.

If we find life in icy moons, then we have to consider that the number of icy dwarf planets in the Kuiper belt, the Oort cloud and the orbits beyond are likely in the thousands. As long as they kept some heat from impacts, nuclear decay or binary tides they may have oceans suitable for life. Impacts carrying life may be rarer up there but they are probably lower speed being in higher orbits, so they'd be more survivable for organisms.