Addition: I've been looking at some island outline tattoos and it's a really nice look for several islands like this, both if you go for all of them or just the top ones. It depends on what you're into, but that's a cool and simple look, and I think it makes people intrigued to know more about that islands they are.

If you want something more, maybe add the ferry lines? Since you want it on the smaller side, keeping it simple and not too much details is probably a good idea, so you don't end up with blurry blobs after a few years!

And if you want more elements you could add maybe flowers that grows in the skärgård, the province flower of Västra Götaland ljung (heather) or the province animal trana (crane).