Floor plan design single-family house with around 150 m²

I also quite like option 1, maybe one could put an armchair under the west window?

Not in addition to the sofa, then it would be way too crowded again.

I also can't get used to the shelf behind the sofa in this version, maybe a wall-mounted solution with a String shelf? And regarding your passage problem, I would maybe also not place the sofa section into the center of the room or at least choose a sofa that is flexible (ottoman or section mountable on both sides). I really like my Vallentuna from the Swedes. Modular system, simple, and nicely deep for lounging; you can start with fewer elements and if you realize it's still not enough, you just buy another one.

Ah, that really makes you want to play Tine Wittler.

And regarding your passage problem, I might also not put the sofa chaise in the middle of the room or at least choose a sofa that is variable (stool or chaise mountable on both sides).

True, that would block the passage. Maybe better on the other side?

Something quite fundamental... would it be worth considering additional windows or window widenings now or sometime in the future, could that give the room even more? I already find it very wall-heavy. Is something like that even possible/feasible and with what effort (could also be a project for the future)? Or can the room also be made to feel spacious enough with design elements so that one doesn’t feel too confined?

Something fundamental... would it be worth thinking now or sometime in the future about additional windows or window widenings, etc., could that give the room even more? I already find it very wall-heavy.

Just put such questions aside until the postnatal depression at least has had its first anniversary, they won’t run away from you. Breathe into a bag until the hyperventilation subsides. Panic doesn’t help now, relax!

I play quite often and find that a piano also adds something to a living space

But not in this case.

I also can’t get used to the shelf behind the sofa in this version,

Me neither. That’s just a demo to show that you could put something there.

And regarding your passage problem, I probably wouldn’t put the sofa section in the middle of the room either

No, exactly, that is the difference between furnishing and just cluttering or sticking it in the corner. And actually, there is no passage problem there. Besides, you can sit in the middle and watch the fireplace blaze. Or turn around and look into the garden. Possibly a simple elongated sofa with a separate cube/footrest, then you’re more flexible.

In any case, one should also consider other shelving units or TV boards. It’s all pointless if you’re not open to changes.

Something very fundamental... would it make sense now or sometime in the future to think about additional windows or widening windows etc., could that add more to the room? I find it already quite wall-heavy.

I wouldn’t think about that yet before other options like the furnishing or color choice have been tried out. Also, you need to experience a summer first to actually know what disadvantages a bigger window can have.

I play quite often and think a piano also adds something to a living space.

Hmm - even if you play the song of the cluttered living space to the living space - doesn't that make it a little sad?