I don't like kullens (the little dimples you probably think of as "Granton"), so don't like the FKS. They don't work for me. You've had advantage with a Granton style knife (Granton edge? Or actualy Granton?), seemed to like it, and that you like it is what counts.
The Fujiwara stainless FKM and FKS series are good quality for their price -- which is entry level. They're good enough knives; better than most of the knives you see in commercial kitchens.
I'd stay far, far away from Fujiwara's carbon FKH series. They don't provide any special benefit for someone in your circumstances, and add a LOT of extra maintenance, not to mention they can discolor and lend an off-aroma to food before they're stabilized (with a patina), but right after sharpening too.
24cm is not an ideal length for a specialty knife used to cut large, super thin slices of fish -- as with gravlax. Longer is very much better. But 24cm and even 21cm, makes a lot of sense for a line knife. If you're only going to have one slicer you've got to choose what works best for you. I used to cut lox with a 10" Sabatier slicer, not to mention all sorts of other portioning, and live to tell the tale. No reason you can't survive 24cm.
Big differences between a yanagiba and suji -- Yanagiba is a stiff, heavy, wide knife. Suji is (wait for it) flexible, light, narrow. If you really concentrated on learning technique you could probably do a slightly better job with a yanigiba than a suji for cutting lox... but it would take some learning, some learning to sharpen, a fairly expensive knife, etc., etc.
The counter-men and women cutting in the few delis I know which still hand slice lox use super long, flexible, inexpensive, specialty knives, like this 12" purpose-made Victorniox Fibrox:
The sushi men I know who do similar cuts use sujis of various sizes during the day, and show off with yanagibas in front of their high-rolling customers at night. I used to hang with a semi-demi-big-deal sushi-ya owner, and he did the same thing. His suji was a 270. The number one guy in the sushi-ya we go to know uses what started as a 240, but is sharpened down to 210. FWIW, when I buy big pieces of cold-smoked fish, or cold-smoke it myself, my current go-to is a (beaucoup expensive) 300. Sometimes I still use one of my old Sabs, but mostly for nostalgia.
If I had the room or reason for another slicer, I'd love one of these:
Although maybe not quite that bent at the handle.
Context, budget and remember Rule 1. Just about anything will do, as long as it's really frikkin' sharp.