ᐅ Y-Tong vs. Concrete Without Additional Insulation in Practice (Heating Costs)

We are about to start building a house using Ytong blocks without additional insulation, with underfloor heating and a heat pump.
Nevertheless, I am interested in this comparison and roughly how much higher heating costs in percentage terms could be expected, if that can even be calculated.
Energy saving is a big focus nowadays. That’s why Ytong was recommended to us, suggesting that extra insulation might not be necessary. The walls can breathe, and the U-value is sufficient. However, the problem with the U-value is that it is a "laboratory value." In practical situations, the sun shines outside, even in winter! Materials with high density like concrete, calcium silicate blocks, etc., are warmed by the sun and can transfer that heat inside the house. Ytong heats up less strongly but retains the interior heat for longer. The same issue applies to triple-glazed windows. They keep the heat inside better but don’t allow the interior space to warm up as much when the sun shines. This puts the U-value into perspective and makes calculating the actual energy consumption for heating somewhat complicated.

If you also factor in air conditioning, which is used in summer to cool a Ytong house, it gets even more complex. Concrete, on the other hand, could keep the interior cooler in summer, potentially allowing one to avoid air conditioning altogether, which saves energy again.

So, it could well be that the difference in heating costs is not as significant as expected in the end. However, with concrete, you might enjoy significantly more comfortable temperatures during the summer.

Does anyone have experience with this? Perhaps someone lives in a concrete house without insulation and can share insights about the indoor climate and heating costs? I would be really interested to hear what comes out of it...