It wouldn't surprise me if he goes for other nearby countries, such as Belarus, Sweden or Finland, western countries that do not belong in the NATO and could potentially be an easier target. He has already threatened Finland and Sweden if they decided to enter NATO.
Belarus is their ally anyway, and they are using their territory to attack Ukraine - so we can say that this is aggression by two countries against one independent country. Unfortunately, it will not be easy for the countries you mentioned to remain intact, because the world has shown that it will not intervene militarily in the defense of any non-NATO country. Even if the two countries are in NATO, the procedure that the military organization has requires all members to give the green light before military action is launched, which can take weeks. It may look good on paper, but in practice, it is a bulky machine that is difficult to start.
This isn't a simple war against Ukraine, but a war against established values we took for granted, which is border integrity and peace, in the European continent, values that till now, were left intact after World War 2.
The EU was weak in 1991 when the wars in the Balkans began, the greatest crimes since World War II were committed - and they imposed sanctions on the attacked countries on arms imports so that they could not defend themselves. The EU is still weak today, and instead of strengthening Ukraine militarily, they are calculating with mostly ineffective sanctions in order not to anger Russia more than they should.