Well, it’s mainly about personal taste here. Almost everyone has booked that for themselves. Personally, I find designer line rooms (or even entire houses) from one manufacturer absolutely terrible. They lack a personal touch. But there’s another reason for me not to do that: it’s hard to replace individual pieces of furniture if you want/find/something breaks. It’s also always difficult to incorporate cherished heirlooms. Something else just doesn’t fit well then. I personally prefer to buy high-quality (often expensive) individual pieces. If the budget isn’t enough, gradually is fine too. These are often timeless in design and still look nice and functional after many years. For example, with my hard-earned money, I bought myself a great wardrobe from Interlübke when I moved out. After 19 years it still looks top-notch and works perfectly (doors, drawers, veneer). Since then the money was all gone, a pallet bed had to suffice first before even that (admittedly from the same manufacturer) was replaced.
There are also more affordable (note, not cheap) high-quality alternatives – for wood, for example, Flötotto or Hülsta (which I personally find very nice) are worth mentioning. You get a lot of use out of them and they bring joy from the very first moment. However, if the house is supposed to be completely furnished and styled from the move-in, that rarely works. It takes time. We are far from finished (with our current apartment – the plot is only just being surveyed, if things go really well – which I unfortunately don’t think – we’ll move in at the end of ’23…), but that is also a big part of the appeal for us. As said, tastes and approaches differ here as much as in house building :)
If you google "design furniture" you’ll also find good dealers who distribute the relevant brands. For inspiration, I also very much enjoy leafing through the Cairo catalog (locus reading), they also have a decent online shop. There you find many inspirations for manufacturers as well.