Now, don't get me wrong, I bloody love the FED 2, but I don't know if that's a step up - more of a step sideways.
You'd be gaining interchangeable lenses, but losing the built-in lightmeter. You're also taking a step-down in terms of optics (the I-26 is probably the worst-performing of the various Soviet "LTM" lenses), and running headlong into the messy issue of "how many idiots have tinkered with this camera and lens over the last 70 years", which Soviet cameras are particularly affected by. There's also the further problem of the fact FEDs aren't cross-compatible with "true" LTM cameras like the Leicas, Canons, Niccas, etc., so whatever you buy in the FED/Zorki world would need to be replaced if you upgraded further later on.
Don't let me put you off - the FED 2 is a great camera and a solid experience (although I'd replace the I-26 with a collapsible Industar 22, personally), but if you were looking for a definite improvement over the Yashica, I'd look elsewhere.
If you have the budget for it, a late Leotax or Nicca with a lever wind would be my choice, personally. They're not quite as pricy as the Leica options, but a damn sight nicer to use than either the Soviet rangefinders or the Canons.
At a lower budget, you've got the Kievs - a bit more esoteric to use than the FED 2, but the lenses are cheaper than the FED equivalents and are much less likely to have been tinkered with over the years. You can also use them on Leicas later with an adapter or on a Contax body without issue, which is something you can't really say about the LTM versions.