One-sided or double-sided fireplace

The sketch is not to scale, I don't remember the exact measurement, but probably around 80 cm? Yes, it is a small room divider.

Well, if you want to be able to sit on the bench with the fireplace fired up, there is hardly any other position. ;-)
We went to an independent fireplace builder. Hark and Co. would have built it that way for us as well for an extra charge, but I don't understand why the bench usually faces the fireplace window there.

Thanks to a power outlet next to the bench, I also regularly sit there in summer (with my phone on the charging cable *g*).
It takes longer in winter to feel warmth on your back, which I also like, than with traditional tiled stoves, but maybe we just kindle too timidly.

A properly sized fireplace also works great in a low-energy house.

Thanks! Did you extend the fireplace up to the ceiling or is there still space above?

Yes, when the fireplace is lit, you probably don’t sit on the bench, but you often see it that way.

You can't determine the correct sizing based on anything here: the living room would currently be the only basis for evaluation, but the OP also wants a conservatory in the future, if I remember correctly - although without any decision yet on if, when, and where :-(

Done right, you can also sit there with a "burning fireplace"