Big DIY chains like Leroy Merlin or Castorama have super complete shelving sections, and you can easily find sleek designs at reasonable prices. You've got floating models in metal or light wood that fit perfectly with a minimalist vibe, and the quality is decent for what you pay. I installed some stuff like that at my place for my aquariums and it holds up fine, even with weight on it. The advantage is you can touch the products before buying, you actually see the finish and dimensions in real life.
Otherwise, there's also marketplaces like Vinted or LeBonCoin if you're looking for solid secondhand stuff - people often resell shelves that are basically brand new because they're changing their décor. You have to check regularly and be quick, but you can snag some really good deals. Small specialized sellers on those platforms also offer stuff like Müller or Scandinavian design that's not too crazy expensive. Mix that with a visit to your local flea market now and then and you should find what you're looking for.