Help me decide on a carpet underlay

[LadyDeGrump]

Getting the carpets replaced in my new flat and need underlay throughout (none currently). We want good noise insulation - airborne and impact - because it is an upstairs flat in a rickety Victorian conversion and I don't want to upset neighbours below or to the sides. Ideally, we would also have a decent level of thermal insulation.

The two brands recommended to me are both Tredaire - 3 Colours Red and Dreamwalk. Dreamwalk is cheaper and does better on thermal but less well on noise. Is 44db protection as opposed to 46 very big?

Does anyone have experience of either and can anyone advise?