You are probably better off continuing to look around. Tiny strips of swamp along mountains are not likely to be big enough to have crypts. As far as the wishbone goes, you would need to defeat bonemass first, and usually there are crypts in a swamp where bonemass is.

You could try sailing next to a swamp, not too close, outside of the fog range and look for the green torches, then keep going and hope to find a black forest or meadows to land and put your portal there. Landing in a swamp itself is generally a bad idea, but sometimes it's hard to find a good swamp that has a good place to land. Beware the plains.