@laumapret I've used spiral steel before and do put in like two flats per every "whalebone" corset, they're just visually thicker (I think the narrowest is 7mm and usually they're wider than that, you can get the whalebone in 3mm and 5mm and wider) and feel a bit different. The spiral steel is much grippier than the whalebone so it's harder on the hands if your boning channels are a bit snug? I've also done the big roll of steels, and while the cutting is possible with some decent hardware aisle cutters it's not so nice on the hands, and what I really struggled with was putting on the end caps nicely. There's a specific pliers for that you sometimes see sold, but that's even more tools. 😄
I wouldn't want to do it with a Karvinen in the space though, that's a lot of tiny metal bits for him to consume.