Lightweight concrete with filling? The agony of choice in masonry

...Aerated concrete is probably out of the question....

Why?

Because soundproofing is poor and he lives in the other 30 km/h zone, where apparently diesel locomotives always pass through at 28.7 km/h.

Oh yes - totally lousy!
And then wanting to live in a 30 km/h zone is just not possible at all!
Only something like at the Adolfbau on Berlin’s Reinhardtstraße works - 3m of reinforced concrete as exterior walls might just be enough.
There is peace in the box and the windowsill area is second to none!

On one side of our property, railcars pass by every half hour. Well... it is 150m from the house to the railway but still.
If a crow sits on the chimney rain cap and sings its fine little song, that is the most perceptible sound source - louder than the rubber-tyred vehicles trying to pass the house on the other side of the property.

Oh yes - totally lousy! And then wanting to live in a 30 km/h zone is just not acceptable at all! Only something like at the Adolfbau in Berlin's Reinhardtstraße works – 3m of reinforced concrete as exterior walls might just be enough. That’s where you have peace and quiet, and the windowsill surface is unparalleled! On one side of our property, railcars pass every half hour. Well... it’s 150m from the house to the railway but still. If a crow sits on the chimney’s rain cap and sings its fine little song, that’s the most noticeable sound source – louder than the rubber-tyred vehicles that want to pass by the house on the other side of the property.

What exactly did you build with?

Outside aerated concrete (monolithic, 36 cm wall), inside sand-lime brick (bulk density 1.8 t/m³) The OP should take the most commonly used building material in their region, or the one preferred by the main builder, and that’s fine. We initially considered using Poroton and then switched to aerated concrete + sand-lime brick for financial reasons. If the OP is afraid of the noise emissions from playing children in autumn and winter, or if things get too loud during sex in the bedroom, sand-lime brick with WVDS plus soundproof glazing helps.

Well, aerated concrete together with decentralized ventilation can be quite loud. And even diesel locomotives at 30km/h can be loud, just ask my wife

When she (many moons ago) slept over at my parents' house for the first time, she was very abruptly woken up at 5:30 in the morning. There is an industrial railway running about 30 meters away, on which potash is transported in full trains from Monday to Saturday. There is a hill by the house, meaning they really rev the 12-cylinder engines of the BR232 Ludmilla right up until just before the house and then ease off the throttle. That even sometimes makes the window panes shake. It was even better with the old locomotives with 16-cylinder engines and whistle fans

You can’t get far with aerated concrete there